68 results on '"Hristov, K."'
Search Results
2. Regional transformations in Bulgaria and challenges for sustainable development
- Author
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Atanasov D., Ivanova B., Beluhova-Uzunova R., Shishkova M., Hristov K., Sharipov S., and Khasanov I.
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Environmental sciences ,GE1-350 - Abstract
Structural changes in rural areas are a subject of widespread discussion. During the transition to a market economy, Bulgarian agriculture underwent serious reforms, and after the accession to the EU, the transformations of the sector became even more significant. Political and socio-economic changes have an impact on agricultural production, organisational structure, and market performance. These processes have played an essential role in the development of rural areas. The aim of the study is based on an analysis of structural changes in Bulgarian agriculture, to outline their impact on the models of transformation of rural areas and make recommendations for sustainable development. Significant changes are observed during the analysed period. The agricultural sector remains polarised and dominated by several significant sub-sectors – cereals and oilseeds. The Common Agricultural Policy (CAP) does not contribute to balanced and sustainable development and deepens disparities. During the new programming period, the opportunities for modelling the CAP are significant and vary considerably. A new conceptual framework needs to be implemented in Bulgaria - the local model related to regional specifics can solve some of the challenges.
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- 2023
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3. Nonperturbative resonant strong field ionization of atomic hydrogen
- Author
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Girju, M. G., Hristov, K., Kidun, O., and Bauer, D.
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Physics - Atomic Physics ,Physics - Optics - Abstract
We investigate resonant strong field ionization of atomic hydrogen with respect to the 1s-2p-transition. By "strong" we understand that Rabi-periods are executed on a femtosecond time scale. Ionization and AC Stark shifts modify the bound state dynamics severely, leading to nonperturbative signatures in the photoelectron spectra. We introduce an analytical model, capable of predicting qualitative features in the photoelectron spectra such as the positions of the Autler-Townes peaks for modest field strengths. Ab initio solutions of the time-dependent Schroedinger equation show a pronounced shift and broadening of the left Autler-Townes peak as the field strength is increased. The right peak remains rather narrow and shifts less. This result is analyzed and explained with the help of exact AC Stark shifts and ionization rates obtained from Floquet theory. Finally, it is demonstrated that in the case of finite pulses as short as 20fs the Autler-Townes duplet can still be resolved. The fourth generation light sources under construction worldwide will provide bright, coherent radiation with photon energies ranging from a tenth of a meV up to tens of keV, hence covering the regime studied in the paper so that measurements of nonperturbative, relative AC Stark shifts should become feasible with these new light sources., Comment: 16 pages, 11 figures, IOP style
- Published
- 2007
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4. REGIONAL DIMENSION OF CHANGES IN BULGARIAN AGRICULTURAL STRUCTURE
- Author
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Beluhova-Uzunova, R., primary, Shishkova, M., additional, and K. Hristov, K. Hristov, additional
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- 2023
- Full Text
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5. Efficacy and safety of retrograde ureteroscopy for the treatment of impacted proximal ureteral stones larger than 10 mm
- Author
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Hristov, K., primary, Petkova, K., additional, Petrova, D., additional, Petrov, P., additional, Hristoforov, S., additional, Gatsev, O., additional, and Saltirov, I., additional
- Published
- 2022
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6. Seroprevalence of Actinobacillus pleuropneumoniae infection in pigs from Bulgaria
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Pepovich, R., primary, Hristov, K., additional, Nikolov, B., additional, Genova, K., additional, Ivanova, E., additional, Kundurzhiev, T., additional, Tsachev, I., additional, Ciccozzi, M., additional, and Baymakova, M., additional
- Published
- 2022
- Full Text
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7. Blood biochemical profiles of dairy cows and their calves from Bulgarian Black and White Cattle Breed
- Author
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Teneva, A., Hristov, K., Georgi Stoimenov, Georgi M Stoimenov, Kalin Hristov, and Georgi Stoimenov
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stomatognathic system ,CP ,blood ,ALAT ,food and beverages ,ALP ,biochemical parameters ,ASAT ,calves - Abstract
This study examined the activities of aspartate aminotransferase (ASAT), alanine aminotrans-ferase (ALAT), alkaline phosphatase (ALP), acid phosphatase (ACP), albumin (Alb), total protein (TP), creatin-phosphokinase (CPK), total lipid (TL), calcium (Ca) in the plasma of 304 dairy Holstein breed cows and their calves. The cows were held in an intensive farm breeding premises. Their meal consisted of ordinary alfalfa, silage, hay and concentrates with energy and protein supplements. The Student t-test showed significant difference (P < 0.05) in mean of the ASAT, ALAT, ALP, ACP, Alb, TP, TL, Ca between cows and calves of the breed. Mean values of the ASAT, ALAT, Alb, TP, TL and Ca was higher in cow group than in calves group (P < 0.05), while ALP and ACP was lower in cow in comparison to the calves group (P < 0.05).
- Published
- 2020
8. STUDY ON THE EFFECTIVENESS OF INTRACISTERNAL ANTIBIOTIC TREATMENT FOR THE CONTROL OF MASTITIS IN GOATS
- Author
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Hristov, K., primary, Pepovich, R., additional, and Nikolov, B., additional
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- 2020
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9. MODELS FOR BALANCED DEVELOPMENT OF BULGARIAN RURAL REGIONS IN THE CONTEXT OF CAP POST-2020
- Author
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Beluhova-Uzunova, R., primary and Hristov, K., additional
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- 2020
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10. MP028 - Efficacy and safety of retrograde ureteroscopy for the treatment of impacted proximal ureteral stones larger than 10 mm
- Author
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Hristov, K., Petkova, K., Petrova, D., Petrov, P., Hristoforov, S., Gatsev, O., and Saltirov, I.
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- 2022
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11. CLINICAL STUDY OF THE CHANGE OF рН LEVEL IN THE SUPRAGINGIVAL PLAQUE IN CHILDREN AFTER TAKING HOMEOPATHIC REMEDIES.
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Pomakova, A., Gateva, N., and Hristov, K.
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- 2021
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12. OBESITY, INFLAMMATION, AND T-CELL METABOLISM
- Author
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Hristov, K., primary
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- 2019
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13. Strategic investment in tuberculosis control in the Republic of Bulgaria
- Author
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Doan, T. N., primary, Varleva, T., additional, Zamfirova, M., additional, Tyufekchieva, M., additional, Keshelava, A., additional, Hristov, K., additional, Yaneva, A., additional, Gadzheva, B., additional, Zhang, S., additional, Irbe, S., additional, Ragonnet, R., additional, McBryde, E. S., additional, and Trauer, J. M., additional
- Published
- 2019
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14. STUDY ON THE EFFECTIVENESS OF INTRACISTERNAL ANTIBIOTIC TREATMENT FOR THE CONTROL OF MASTITIS IN GOATS.
- Author
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Hristov, K., Pepovich, R., Nikolov, B., and Stoimenov, G.
- Subjects
- *
MASTITIS , *GOATS , *SOMATIC cells , *HEALING , *EXPERIMENTAL groups , *ANTIBIOTICS - Abstract
The aim of this study is to investigate the healing and prophylactic effect of drying-off antibiotic therapy using the selective and non-selective approach of administration of the antibiotics. First experimental group at the start of the dry period were treated non-selectively (all halves) intracisternally with antibiotics. In the second group, we only treated those halves that were diagnosed with subclinical mastitis. The control group of 9 goats was not treated. The number of somatic cells in treated groups after birth decreased from 2586 x 10³/ mL to 560 x 10³/mL in the first group and from 1978 x 10³/mL to 526 x 10³/mL in the second. Post partum, 10% of the halves were found to have subclinical mastitis. A healing effect was achieved in 25% (n=5) milk halves. New intramammary infections developed during the dry period also occurred in 5% (n=1) of the milk halves. In the second post-partum study, subclinical mastitis was observed only in 5% (n=1). Healing was achieved in 30% (n = 6) and the new intramammary infections (NIMIs) were 10% (n=2). In the control group, healing was only observed in 5% (n=1) and NIMI were 27.78% (n=5). The application of both treatment approaches, results in reduction in prevalence and manifestation of mastitis, as well as reduction of somatic cells in milk after kidding. The selective treatment method may be preferred, in order to reduce the cost of medications in conducting treatment and prophylaxis programs. [ABSTRACT FROM AUTHOR]
- Published
- 2020
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15. Rotating black holes in 4d gauged supergravity
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Gnecchi, A., Hristov, K., Klemm, D., Toldo, C., Vaughan, O., Theoretical Physics, Sub String Theory Cosmology and ElemPart, Quantum Gravity, Strings and Elementary Particles, Gnecchi, A, Hristov, K, Klemm, D, Toldo, C, Vaughan, O, Theoretical Physics, Sub String Theory Cosmology and ElemPart, and Quantum Gravity, Strings and Elementary Particles
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High Energy Physics - Theory ,Physics ,Large class ,Angular momentum ,Nuclear and High Energy Physics ,Scalar (mathematics) ,Gauged supergravity ,Superstring Vacua ,FOS: Physical sciences ,General Relativity and Quantum Cosmology (gr-qc) ,AdS-CFT Correspondence ,General Relativity and Quantum Cosmology ,Black hole ,Theoretical physics ,High Energy Physics - Theory (hep-th) ,Black Holes in String Theory - Abstract
We present new results towards the construction of the most general black hole solutions in four-dimensional Fayet-Iliopoulos gauged supergravities. In these theories black holes can be asymptotically AdS and have arbitrary mass, angular momentum, electric and magnetic charges and NUT charge. Furthermore, a wide range of horizon topologies is allowed (compact and noncompact) and the complex scalar fields have a nontrivial radial and angular profile. We construct a large class of solutions in the simplest single scalar model with prepotential $F = -i X^0 X^1$ and discuss their thermodynamics. Moreover, various approaches and calculational tools for facing this problem with more general prepotentials are presented., Comment: 37 pages, 1 figure
- Published
- 2014
16. Some parasitological, pathological and immunohistochemical examinations in sheep naturally infected by Trichuris ovis
- Author
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Iliev, P., primary, Ivanov, A., additional, Kirkova, Z., additional, Hristov, K., additional, Dinkova, K., additional, and Ananiev, J., additional
- Published
- 2017
- Full Text
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17. Analisys of direct payments distribution in Bulgarian agriculture
- Author
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Beluhova-Uzunova, R., primary, Atanasov, D., additional, and Hristov, K., additional
- Published
- 2017
- Full Text
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18. Phase transitions of magnetic AdS4 black holes with scalar hair
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Hristov, K., Toldo, C., Vandoren, S., Theoretical Physics, Sub String Theory Cosmology and ElemPart, Theoretical Physics, Sub String Theory Cosmology and ElemPart, Hristov, K, Toldo, C, and Vandoren, S
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Physics ,High Energy Physics - Theory ,Nuclear and High Energy Physics ,Particle physics ,010308 nuclear & particles physics ,Astrophysics::High Energy Astrophysical Phenomena ,Gauged supergravity ,FOS: Physical sciences ,Charged black hole ,01 natural sciences ,Black hole ,Micro black hole ,High Energy Physics::Theory ,General Relativity and Quantum Cosmology ,High Energy Physics - Theory (hep-th) ,0103 physical sciences ,Extremal black hole ,Black brane ,010306 general physics ,Black hole thermodynamics ,Hawking radiation ,Mathematical physics - Abstract
We determine the thermodynamic properties of a class of spherically symmetric and static black holes in AdS4 with magnetic charges and scalar hair. These black holes are solutions in 4d N=2 gauged supergravity that can arise from eleven-dimensional supergravity compactified on S^7. At zero temperature, they preserve supersymmetry and hence are stable. At non-zero temperatures, we explore in detail the canonical ensemble and stability of solutions and find a first order phase transition between small and large hairy black holes. The transition emerges as a liquid-gas phase transition in the dual three-dimensional field theory on R x S^2 with magnetic flux through S^2., 5 pages, v2: misprints corrected and references added, published version
- Published
- 2013
19. Lessons from the Vacuum Structure of 4d N=2 Supergravity
- Author
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Hristov, K., Theoretical Physics, Sub String Theory Cosmology and ElemPart, Vandoren, Stefan, and University Utrecht
- Subjects
High Energy Physics::Theory ,General Relativity and Quantum Cosmology - Abstract
This thesis is devoted to a study of supersymmetry preserving background solutions of N=2 supergravity in 4 dimensions. These models include arbitrary electric gaugings in the vector- and hypermultiplet sectors introduced in the beginning of the thesis. The main contents are divided into three major parts. In part 1 we consider vacua that can be fully analyzed by requiring preserved supersymmetry. We determine and analyze maximally supersymmetric configurations, preserving eight supercharges. We present several examples of such solutions and connect some of them to vacuum solutions of flux compactifications in string theory. We also provide a consistent truncation of the gauged theory based on integrating out massive supermultiplets of the gauged theory. The second part is devoted to the topic of supersymmetric black holes. These can be asymptotically flat or asymptotically AdS, and we analyze both cases in detail. We construct BPS black hole solutions in Minkowski space with charged hypermultiplets. We find solutions with vanishing scalar hair that resemble already known black holes, while the genuinely new solutions with hair that we find contain ghost modes. We also elaborate further on the static supersymmetric AdS black holes found in arXiv:0911.4926, investigating thoroughly the BPS constraints for spherical symmetry in N = 2 gauged supergravity. We find Killing spinors that preserve two of the original eight supercharges and investigate the conditions for genuine black holes free of naked singularities. The existence of a horizon is intimately related with the requirement that the scalars are not constant, but given in terms of harmonic functions in analogy to the attractor flow in ungauged supergravity. The third major topic of this thesis is BPS bounds, where we discuss asymptotically Minkowski and AdS solutions in full generality. We concentrate on asymptotically anti-de Sitter (AdS) spacetimes, and find that there exist two disconnected BPS ground states of the theory, depending on the presence of magnetic charge. Each of these ground states comes with a different superalgebra and a different BPS bound, which we derive. As a byproduct, we also demonstrate how the supersymmetry algebra has a built-in holographic renormalization method to define finite conserved charges. We derive the general form of the charges for all asymptotically flat, anti-de Sitter, and magnetic anti-de Sitter spacetimes. Some particular black hole examples from part 2 are considered to explicitly demonstrate how AdS and mAdS masses differ when solutions with non-trivial scalar profiles are considered
- Published
- 2012
20. Black branes in AdS: BPS bounds and asymptotic charges
- Author
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Hristov, K., Toldo, C., Vandoren, S., Theoretical Physics, and Sub String Theory Cosmology and ElemPart
- Subjects
High Energy Physics - Theory ,High Energy Physics::Theory ,General Relativity and Quantum Cosmology ,High Energy Physics - Theory (hep-th) ,Astrophysics::High Energy Astrophysical Phenomena ,FOS: Physical sciences - Abstract
We focus on black branes and toroidal black holes in N=2 gauged supergravities that asymptote to AdS_4, and derive formulas for the mass and central charge densities. We derive the corresponding BPS bound from the superalgebra of the asymptotic vacuum and illustrate our procedure with explicit examples of genuine black brane solutions with non-trivial scalars., Comment: 9 pages, Contribution to the proceedings of the "XVII European Workshop on String Theory 2011", Padova, Italy, 5-9 September 2011
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- 2012
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21. On BPS bounds in D=4 N=2 gauged supergravity
- Author
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Hristov, K., Toldo, C., Vandoren, S.J.G., Theoretical Physics, and Sub String Theory Cosmology and ElemPart
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High Energy Physics - Theory ,Physics ,Nuclear and High Energy Physics ,Spacetime ,010308 nuclear & particles physics ,Gauged supergravity ,Magnetic monopole ,FOS: Physical sciences ,01 natural sciences ,Superalgebra ,Renormalization ,General Relativity and Quantum Cosmology ,High Energy Physics::Theory ,High Energy Physics - Theory (hep-th) ,0103 physical sciences ,010306 general physics ,Supersymmetry algebra ,Mathematical physics - Abstract
We determine the BPS bounds in minimal gauged supergravity in four spacetime dimensions. We concentrate on asymptotically anti-de Sitter (AdS) spacetimes, and find that there exist two disconnected BPS ground states of the theory, depending on the presence of magnetic charge. Each of these ground states comes with a different superalgebra and a different BPS bound, which we derive. As a byproduct, we also demonstrate how the supersymmetry algebra has a built-in holographic renormalization method to define finite conserved charges., Comment: 23 pages; v2 typos corrected, published version; v3 typos in Eqs. (3.6) and (3.31) corrected
- Published
- 2011
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22. Maximally supersymmetric solutions of D = 4 N = 2 gauged supergravity
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Hristov, K., Looyestijn, H.T., Vandoren, S.J.G., Instituut Theoretische Fysica, Theoretical Physics, and Sub String Theory Cosmology and ElemPart
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High Energy Physics::Theory ,High Energy Physics::Phenomenology - Abstract
We determine and analyze maximally supersymmetric configurations in four-dimensional gauged N = 2 supergravity, preserving eight supercharges. These models include arbitrary electric gaugings in the vector- and hypermultiplet sectors. We present several examples of such solutions and connect some of them to vacuum solutions of flux compactifications in string theory.
- Published
- 2009
23. Axion stabilization in type IIB flux compactifications
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Hristov, K., Instituut Theoretische Fysica, and Sub String Theory Cosmology and ElemPart
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High Energy Physics::Theory ,Mathematics::Algebraic Geometry ,High Energy Physics::Phenomenology ,Mathematics::Symplectic Geometry - Abstract
A scenario for stabilization of axionic moduli fields in the context of type IIB Calabi-Yau flux compactifications is discussed in detail. We consider the case of a Calabi-Yau orientifold with h1,1−≠0 which allows for the presence of B2 and C2-moduli. In an attempt to generalize the KKLT and the Large Volume Scenario, we show that these axions can also be stabilized - some already at tree level, and others when we include perturbative α'-corrections to the Kähler potential K and nonperturbative D3-instanton contributions to the superpotential W. At last, we comment on the possible influence of worldsheet instantons on the process of moduli stabilization.
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- 2009
24. Comparing institutional and organizational design of Currency Boards in transition countries
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Hristov, K., Mihaylov, M., Nenovsky, Nikolay, Laboratoire d'Économie d'Orleans [UMR6586] (LEO), Université d'Orléans (UO)-Centre National de la Recherche Scientifique (CNRS), and Laboratoire d'Économie d'Orleans (LEO)
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design ,organizational ,Boards ,Comparing ,transition ,countries ,[SHS.ECO]Humanities and Social Sciences/Economics and Finance ,Currency ,institutional - Published
- 2002
25. Some season-related morphometric, structural and weight characteristics of testes in the viper (Vipera ammodytes)
- Author
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Dimitrov, D., Hristov, K., and Angelov, A.
- Subjects
eason-related characteristics ,testes ,viper - Abstract
The study was performed on testes, obtained from 14 vipers (Vipera ammodytes), inhabiting various regions of Bulgaria, collected during the four seasons of the period 1996-1999 inclusive. The weight and the macrometric parameters of testes were measured. The outer diameter of seminiferous tubules and season-related microstructural features were determined via light microscopy. Data from weight, metric and micrometric measurements were statistically processed. Their analysis showed that from winter to the end of spring (when the breding period of vipers in Bulgaria occurs), the weight of testes increased more than thrice, the diameter of seminiferous tubules - more than twice and afterwards the values of both parameters decreased gradually and reached the highest values for the winter season by the end of the autumn. The seasonal variations in both weight and diameter correlated with the histological status of testes. The involution processes within seminiferous tubules, starting by the beginning of winter, were still active also in the middle or end of spring, when vipers were ready again for another reproductive period.
- Published
- 2002
26. BPS black holes in N=2 D=4 gauged supergravities
- Author
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Hristov, K., Looyestijn, H.T., Vandoren, S.J.G., Theoretical Physics, and Sub String Theory Cosmology and ElemPart
- Subjects
High Energy Physics - Theory ,Physics ,Nuclear and High Energy Physics ,Spontaneous symmetry breaking ,Supergravity ,Astrophysics::High Energy Astrophysical Phenomena ,Scalar (mathematics) ,FOS: Physical sciences ,Supersymmetry ,Black hole ,High Energy Physics::Theory ,General Relativity and Quantum Cosmology ,High Energy Physics - Theory (hep-th) ,Axial symmetry ,Multiplet ,Mathematical physics - Abstract
We construct and analyze BPS black hole solutions in gauged N=2, D=4 supergravity with charged hypermultiplets. A class of solutions can be found through spontaneous symmetry breaking in vacua that preserve maximal supersymmetry. The resulting black holes do not carry any hair for the scalars. We demonstrate this with explicit examples of both asymptotically flat and anti-de Sitter black holes. Next, we analyze the BPS conditions for asymptotically flat black holes with scalar hair and spherical or axial symmetry. We find solutions only in cases when the metric contains ripples and the vector multiplet scalars become ghost-like. We give explicit examples that can be analyzed numerically. Finally, we comment on a way to circumvent the ghost-problem by introducing also fermionic hair., 40 pages, 2 figures; v2 references added; v3 minor changes, published version
- Published
- 2010
27. Genetic Variation Within and Among Populations of Maize Inbred B37 Revealed By SSR Markers
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Kostova, A., primary, Todorovska, E., additional, Christov, N., additional, Hristov, K., additional, Jacquemin, J.-M., additional, Muhovski, Y., additional, and Atanassov, A.I., additional
- Published
- 2006
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28. Rotating multi-charge spindles and their microstates
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Alberto Zaffaroni, Seyed Morteza Hosseini, Kiril Hristov, Hosseini, S, Hristov, K, and Zaffaroni, A
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Polynomial (hyperelastic model) ,Physics ,High Energy Physics - Theory ,Nuclear and High Energy Physics ,Conformal Field Theory ,010308 nuclear & particles physics ,Conformal field theory ,FOS: Physical sciences ,Charge (physics) ,Conical surface ,QC770-798 ,AdS-CFT Correspondence ,01 natural sciences ,Supersymmetric Gauge Theory ,AdS/CFT correspondence ,High Energy Physics::Theory ,High Energy Physics - Theory (hep-th) ,Supersymmetric gauge theory ,Nuclear and particle physics. Atomic energy. Radioactivity ,0103 physical sciences ,Black Holes in String Theory ,Gravitational singularity ,Anomaly (physics) ,010306 general physics ,Mathematical physics - Abstract
Some AdS$_3 \times M_7$ type IIB vacua have been recently proposed to arise from D3-branes wrapped on a spindle, a sphere with conical singularities at the poles. We explicitly construct a generalization of these solutions corresponding to a class of electrically charged and rotating supersymmetric black strings in AdS$_5 \times S^5$ with general magnetic fluxes on the spindle. We then perform a counting of their microstates using the charged Cardy formula. To this purpose, we derive the general form of the anomaly polynomial of the dual $\mathcal{N} = (0 , 2)$ CFT in two dimensions and we show that it can be obtained via a simple gluing procedure., 39 pages, v2: references added
- Published
- 2021
29. Anomalies, black strings and the charged Cardy formula
- Author
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Yuji Tachikawa, Alberto Zaffaroni, Seyed Morteza Hosseini, Kiril Hristov, Hosseini, S, Hristov, K, Tachikawa, Y, and Zaffaroni, A
- Subjects
Physics ,High Energy Physics - Theory ,Nuclear and High Energy Physics ,010308 nuclear & particles physics ,Riemann surface ,FOS: Physical sciences ,Sigma ,Field Theories in Higher Dimensions ,AdS-CFT Correspondence ,01 natural sciences ,symbols.namesake ,AdS/CFT correspondence ,General Relativity and Quantum Cosmology ,High Energy Physics - Theory (hep-th) ,Black Holes in String Theory ,0103 physical sciences ,Black string ,symbols ,lcsh:QC770-798 ,lcsh:Nuclear and particle physics. Atomic energy. Radioactivity ,Anomalies in Field and String Theorie ,Anomalies in Field and String Theories ,010306 general physics ,Mathematical physics - Abstract
We derive the general anomaly polynomial for a class of two-dimensional CFTs arising as twisted compactifications of a higher-dimensional theory on compact manifolds $\mathcal{M}_d$, including the contribution of the isometries of $\mathcal{M}_d$. We then use the result to perform a counting of microstates for electrically charged and rotating supersymmetric black strings in AdS$_5\times S^5$ and AdS$_7\times S^4$ with horizon topology BTZ$ \ltimes S^2$ and BTZ$ \ltimes S^2 \times \Sigma_\mathfrak{g}$, respectively, where $\Sigma_\mathfrak{g}$ is a Riemann surface. We explicitly construct the latter class of solutions by uplifting a class of four-dimensional rotating black holes. We provide a microscopic explanation of the entropy of such black holes by using a charged version of the Cardy formula., Comment: 42 pages, 1 figure; v2: crucial references added; v3: typos corrected
- Published
- 2020
30. Holographic microstate counting for AdS4 black holes in massive IIA supergravity
- Author
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Seyed Morteza Hosseini, Achilleas Passias, Kiril Hristov, Hosseini, S, Hristov, K, and Passias, A
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High Energy Physics - Theory ,Nuclear and High Energy Physics ,Particle physics ,Black hole ,Astrophysics::High Energy Astrophysical Phenomena ,FOS: Physical sciences ,Supersymmetric localization ,01 natural sciences ,Gauge-gravity correspondence ,Supersymmetric Gauge Theory ,General Relativity and Quantum Cosmology ,High Energy Physics::Theory ,0103 physical sciences ,Black Holes in String Theory ,Fysik ,lcsh:Nuclear and particle physics. Atomic energy. Radioactivity ,Twist ,010306 general physics ,Black hole thermodynamics ,Entropy (arrow of time) ,Physics ,AdS/CFT correspondence ,010308 nuclear & particles physics ,Supergravity ,High Energy Physics::Phenomenology ,Supersymmetry ,Dyon ,High Energy Physics - Theory (hep-th) ,Supersymmetric gauge theory ,Physical Sciences ,lcsh:QC770-798 ,Ground state - Abstract
We derive the Bekenstein-Hawking entropy for a class of BPS black holes in the massive type IIA supergravity background AdS$_4 \times S^6$ from a microscopic counting of supersymmetric ground states in a holographically dual field theory. The counting is performed by evaluating the topologically twisted index of three-dimensional $\mathcal{N}=2$ Chern-Simons-matter gauge theories in the large $N$ limit. The $\mathcal{I}$-extremization principle is shown to match the attractor mechanism for the near-horizon geometries constructed in the four-dimensional dyonic $\mathcal{N}=2$ gauged supergravity, that arises as a consistent truncation of massive type IIA supergravity on $S^6$. In particular, our results prove that the imaginary part of the three-dimensional partition functions plays a crucial r\^ole in holography., Comment: 33 pages; v2: ref added, typos corrected; v3: published version
- Published
- 2017
31. An extremization principle for the entropy of rotating BPS black holes in AdS5
- Author
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Alberto Zaffaroni, Seyed Morteza Hosseini, Kiril Hristov, Hosseini, S, Kiril Hristov, K, and Zaffaroni, A
- Subjects
High Energy Physics - Theory ,Nuclear and High Energy Physics ,FOS: Physical sciences ,AdS-CFT Correspondence ,01 natural sciences ,General Relativity and Quantum Cosmology ,High Energy Physics::Theory ,0103 physical sciences ,Black Holes in String Theory ,Supergravity Model ,lcsh:Nuclear and particle physics. Atomic energy. Radioactivity ,010306 general physics ,Black hole thermodynamics ,Entropy (arrow of time) ,Mathematical physics ,Physics ,010308 nuclear & particles physics ,Supergravity ,Gauged supergravity ,Supersymmetry ,Casimir effect ,AdS/CFT correspondence ,High Energy Physics - Theory (hep-th) ,lcsh:QC770-798 ,Anti-de Sitter space ,Supergravity Models - Abstract
We show that the Bekenstein-Hawking entropy of a class of BPS electrically charged rotating black holes in AdS$_5\times S^5$ can be obtained by a simple extremization principle. We expect that this extremization corresponds to the attractor mechanism for BPS rotating black holes in five-dimensional gauged supergravity, which is still unknown. The expression to be extremized has a suggestive resemblance to anomaly polynomials and the supersymmetric Casimir energy recently studied for $\mathcal{N}=4$ super Yang-Mills., Comment: 27 pages; v2: refs added; v3: ref added
- Published
- 2017
32. 6D attractors and black hole microstates
- Author
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Achilleas Passias, Seyed Morteza Hosseini, Kiril Hristov, Alberto Zaffaroni, Hosseini, S, Hristov, K, Passias, A, and Zaffaroni, A
- Subjects
High Energy Physics - Theory ,Nuclear and High Energy Physics ,FOS: Physical sciences ,AdS-CFT Correspondence ,01 natural sciences ,Subatomär fysik ,symbols.namesake ,High Energy Physics::Theory ,General Relativity and Quantum Cosmology ,Subatomic Physics ,0103 physical sciences ,Attractor ,Black Holes in String Theory ,lcsh:Nuclear and particle physics. Atomic energy. Radioactivity ,Supergravity Model ,010306 general physics ,Multiplet ,Mathematical physics ,Physics ,010308 nuclear & particles physics ,Supergravity ,Riemann surface ,Gauged supergravity ,High Energy Physics::Phenomenology ,Black hole ,Constant curvature ,AdS/CFT correspondence ,High Energy Physics - Theory (hep-th) ,symbols ,lcsh:QC770-798 ,Supergravity Models - Abstract
We find a family of AdS$_2\times \mathcal{M}_4$ supersymmetric solutions of the six-dimensional $\mathrm{F}(4)$ gauged supergravity coupled to one vector multiplet that arises as a low energy description of massive type IIA supergravity on (warped) AdS$_6\times S^4$. $\mathcal{M}_4$ is either a K\"ahler-Einstein manifold or a product of two Riemann surfaces with a constant curvature metric. These solutions correspond to the near-horizon region of a family of static magnetically charged black holes. In the case where $\mathcal{M}_4$ is a product of Riemann surfaces, we successfully compare their entropy to a microscopic counting based on the recently computed topologically twisted index of the five-dimensional $\mathcal{N}=1$ $\mathrm{USp}(2 N)$ theory with $N_f$ fundamental flavors and an antisymmetric matter field. Furthermore, our results suggest that the near-horizon regions exhibit an attractor mechanism for the scalars in the matter coupled $\mathrm{F}(4)$ gauged supergravity, and we give a proposal for it., Comment: 19 pages, v2: minor corrections
- Published
- 2019
33. Microstates of rotating AdS5 strings
- Author
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Alberto Zaffaroni, Seyed Morteza Hosseini, Kiril Hristov, Hosseini, S, Hristov, K, and Zaffaroni, A
- Subjects
High Energy Physics - Theory ,Physics ,Nuclear and High Energy Physics ,Conformal Field Theory ,010308 nuclear & particles physics ,Gauged supergravity ,Fibration ,FOS: Physical sciences ,Conical surface ,AdS-CFT Correspondence ,01 natural sciences ,Supersymmetric Gauge Theory ,General Relativity and Quantum Cosmology ,High Energy Physics - Theory (hep-th) ,0103 physical sciences ,Homogeneous space ,Black Holes in String Theory ,Entropy (information theory) ,lcsh:QC770-798 ,Gravitational singularity ,lcsh:Nuclear and particle physics. Atomic energy. Radioactivity ,Gauge theory ,Twist ,010306 general physics ,Mathematical physics - Abstract
We provide a general formula for the refined topologically twisted index of $\mathcal{N}=1$ gauge theories living on the world-volume of D3-branes at conical Calabi-Yau singularities in the Cardy limit. The index is defined as the partition function on $T^2 \times S^2_\omega$, with a partial topological twist and a $\Omega$-deformation along $S^2$, in the presence of background magnetic fluxes and fugacities for the global symmetries and can be used to study the properties of a class of BPS black strings. To this purpose, we find rotating domain-wall solutions of five-dimensional gauged supergravity interpolating between AdS$_5$ and a near horizon region consisting of a warped fibration of BTZ over a sphere. We explicitly construct rotating domain-walls that can be embedded in AdS$_5 \times S^5$ by uplifting a class of four-dimensional rotating black holes. We then provide a microscopic explanation of the entropy of such black holes by using the refined topologically twisted index of $\mathcal{N}=4$ super Yang-Mills., Comment: 31 pages; v2: typos corrected
- Published
- 2019
34. Gluing gravitational blocks for AdS black holes
- Author
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Kiril Hristov, Alberto Zaffaroni, Seyed Morteza Hosseini, Hosseini, S, Hristov, K, and Zaffaroni, A
- Subjects
High Energy Physics - Theory ,Physics ,Nuclear and High Energy Physics ,010308 nuclear & particles physics ,Astrophysics::High Energy Astrophysical Phenomena ,Holomorphic function ,FOS: Physical sciences ,AdS-CFT Correspondence ,01 natural sciences ,Gravitation ,Theoretical physics ,AdS/CFT correspondence ,General Relativity and Quantum Cosmology ,High Energy Physics - Theory (hep-th) ,Factorization ,0103 physical sciences ,Attractor ,Black Holes in String Theory ,lcsh:QC770-798 ,lcsh:Nuclear and particle physics. Atomic energy. Radioactivity ,Twist ,010306 general physics ,Supergravity Models - Abstract
We provide a unifying entropy functional and an extremization principle for black holes and black strings in AdS$_4\times S^7$ and AdS$_5\times S^5$ with arbitrary rotation and generic electric and magnetic charges. This is done by gluing gravitational blocks, basic building blocks that are directly inspired by the holomorphic blocks appearing in the factorization of supersymmetric partition functions in three and four dimensions. We also provide an explicit realization of the attractor mechanism by identifying the values of the scalar fields at the horizon with the critical points of the entropy functional. We give examples based on dyonic rotating black holes with a twist in AdS$_4\times S^7$, rotating black strings in AdS$_5\times S^5$, dyonic Kerr-Newman black holes in AdS$_4\times S^7$ and Kerr-Newman black holes in AdS$_5\times S^5$. In particular, our entropy functional extends existing results by adding rotation to the twisted black holes in AdS$_4$ and by adding flavor magnetic charges for the Kerr-Newman black holes in AdS$_4$. We also discuss generalizations to higher-dimensional black objects., 44 pages, v2: Published version, (6.17) corrected; v3: typos corrected
- Published
- 2019
- Full Text
- View/download PDF
35. Exact microstate counting for dyonic black holes in AdS4
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Kiril Hristov, Francesco Benini, Alberto Zaffaroni, Benini, F, Hristov, K, and Zaffaroni, A
- Subjects
High Energy Physics - Theory ,Physics ,Nuclear and High Energy Physics ,010308 nuclear & particles physics ,Gauged supergravity ,FOS: Physical sciences ,High Energy Physic ,gauge theorie ,String theory ,01 natural sciences ,lcsh:QC1-999 ,Settore FIS/02 - Fisica Teorica, Modelli e Metodi Matematici ,Theoretical physics ,High Energy Physics::Theory ,General Relativity and Quantum Cosmology ,Ministate ,High Energy Physics - Theory (hep-th) ,Quantum mechanics ,0103 physical sciences ,Attractor ,Quantum gravity ,string theory ,Gauge theory ,010306 general physics ,lcsh:Physics - Abstract
We present a counting of microstates of a class of dyonic BPS black holes in AdS$_4$ which precisely reproduces their Bekenstein-Hawking entropy. The counting is performed in the dual boundary description, that provides a non-perturbative definition of quantum gravity, in terms of a twisted and mass-deformed ABJM theory. We evaluate its twisted index and propose an extremization principle to extract the entropy, which reproduces the attractor mechanism in gauged supergravity., Comment: 4 pages
- Published
- 2017
36. 6d → 5d → 4d reduction of BPS attractors in flat gauged supergravities
- Author
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Andrea Rota, Kiril Hristov, Hristov, K, and Rota, A
- Subjects
High Energy Physics - Theory ,Physics ,Nuclear and High Energy Physics ,Supergravity ,Gauged supergravity ,Kaluza–Klein theory ,FOS: Physical sciences ,String theory ,Black hole ,General Relativity and Quantum Cosmology ,High Energy Physics::Theory ,High Energy Physics - Theory (hep-th) ,Quantum electrodynamics ,Attractor ,Black string ,lcsh:QC770-798 ,lcsh:Nuclear and particle physics. Atomic energy. Radioactivity ,Central charge ,Mathematical physics - Abstract
Via a series of Kaluza-Klein (KK) and Scherk-Schwarz (SS) compactifications we relate BPS attractors and their complete (in general non-BPS) flows to a Minkowski vacuum in gauged supergravities with vanishing scalar potential in 4, 5, and 6 dimensions. This way we can look at a class of extremal non-BPS black holes and strings from IIB string theory viewpoint, keeping 4 supercharges on the horizon. Our results imply the existence of a dual 2d N = (0,2) superconformal field theory (SCFT) that originates from a parent N=(4,4) theory living on a D1-D5 system. This is achieved starting from the BPS black string in 6d with an AdS_3xS^3 attractor and taking two different routes to arrive at a 1/2 BPS AdS_2xS^2 attractor of a non-BPS black hole in 4d N=2 flat gauged supergravity. The two inequivalent routes interchange the order of KK reduction on AdS_3 and SS reduction on S^3. We also find the commutator between the two operations after performing a duality transformation: on the level of the theory the result is the exchange of electric with magnetic gaugings; on the level of the solution we find a flip of the quartic invariant I_4 to -I_4., Comment: 20 pages, 2 flow charts; v2 improved discussion and added reference
- Published
- 2015
37. Ungauging black holes and hidden supercharges
- Author
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Valentina Pozzoli, Kiril Hristov, Stefanos Katmadas, Hristov, K, Katmadas, S, and Pozzoli, V
- Subjects
Physics ,High Energy Physics - Theory ,Nuclear and High Energy Physics ,010308 nuclear & particles physics ,Supergravity ,Astrophysics::High Energy Astrophysical Phenomena ,High Energy Physics::Phenomenology ,FOS: Physical sciences ,Scalar potential ,Keywords: Black Hole ,01 natural sciences ,Theoretical physics ,High Energy Physics::Theory ,General Relativity and Quantum Cosmology ,High Energy Physics - Theory (hep-th) ,0103 physical sciences ,Minkowski space ,Supergravity Model ,Abelian group ,010306 general physics ,Entropy (arrow of time) - Abstract
We embed the general solution for non-BPS extremal asymptotically flat static and under-rotating black holes in abelian gauged D=4 N=2 supergravity, in the limit where the scalar potential vanishes but the gauging does not. Using this result, we show explicitly that some supersymmetries are preserved in the near horizon region of all the asymptotically flat solutions above, in the gauged theory. This reveals a deep relation between microscopic entropy counting of extremal black holes in Minkowski and BPS black holes in AdS. Finally, we discuss the relevance of this construction to the structure of asymptotically AdS4 black holes, as well as the possibility of including hypermultiplets., Comment: 33 pages, 1 figure, v2: Corrections in section 5, comments added, references updated
- Published
- 2013
38. Attractors, black objects, and holographic RG flows in 5d maximal gauged supergravities
- Author
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Andrea Rota, Kiril Hristov, Hristov, K, and Rota, A
- Subjects
Physics ,High Energy Physics - Theory ,Nuclear and High Energy Physics ,Scalar (mathematics) ,Holography ,FOS: Physical sciences ,AdS-CFT Correspondence ,law.invention ,Theoretical physics ,High Energy Physics::Theory ,General Relativity and Quantum Cosmology ,High Energy Physics - Theory (hep-th) ,law ,De Sitter universe ,Minkowski space ,Attractor ,Black Holes in String Theory ,Brane cosmology ,Supergravity Model ,Systematic search - Abstract
We perform a systematic search for static solutions in different sectors of 5d $N=8$ supergravities with compact and non-compact gauged R-symmetry groups, finding new and listing already known backgrounds. Due to the variety of possible gauge groups and resulting scalar potentials, the maximally symmetric vacua we encounter in these theories can be Minkowski, de Sitter, or anti-de Sitter. There exist BPS and non-BPS near-horizon geometries and full solutions with all these three types of asymptotics, corresponding to black holes, branes, strings, rings, and other black objects with more exotic horizon topologies, supported by $U(1)$ and $SU(2)$ charges. The asymptotically AdS$_5$ solutions also have a clear holographic interpretation as RG flows of field theories on D3 branes, wrapped on compact 2- and 3-manifolds., Comment: 38 pages, 3 figures, 7 tables
- Published
- 2013
- Full Text
- View/download PDF
39. Supersymmetry on Three-dimensional Lorentzian Curved Spaces and Black Hole Holography
- Author
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Alessandro Tomasiello, Alberto Zaffaroni, Kiril Hristov, Hristov, K, Tomasiello, A, and Zaffaroni, A
- Subjects
High Energy Physics - Theory ,Physics ,Nuclear and High Energy Physics ,Spinor ,Black Holes ,010308 nuclear & particles physics ,Graviphoton ,Magnetic monopole ,FOS: Physical sciences ,Conformal map ,Supersymmetry ,AdS-CFT Correspondence ,01 natural sciences ,Black hole ,Supersymmetric gauge theory ,Killing vector field ,Theoretical physics ,High Energy Physics::Theory ,General Relativity and Quantum Cosmology ,High Energy Physics - Theory (hep-th) ,Killing spinor ,0103 physical sciences ,010306 general physics - Abstract
We study N, 40 pages, no figures; v2 typos corrected
- Published
- 2013
40. Black hole microstates in AdS4 from supersymmetric localization
- Author
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Alberto Zaffaroni, Kiril Hristov, Francesco Benini, Benini, F, Hristov, K, and Zaffaroni, A
- Subjects
High Energy Physics - Theory ,Class (set theory) ,Nuclear and High Energy Physics ,Black Holes ,Astrophysics::High Energy Astrophysical Phenomena ,FOS: Physical sciences ,General Relativity and Quantum Cosmology (gr-qc) ,AdS-CFT Correspondence ,01 natural sciences ,General Relativity and Quantum Cosmology ,Supersymmetric gauge theory ,Theoretical physics ,Nonperturbative Effects ,0103 physical sciences ,Field theory (psychology) ,Limit (mathematics) ,010306 general physics ,Physics ,010308 nuclear & particles physics ,Entropy (statistical thermodynamics) ,Black Hole ,Settore FIS/02 - Fisica Teorica, Modelli e Metodi Matematici ,Black hole ,FIS/02 - FISICA TEORICA, MODELLI E METODI MATEMATICI ,High Energy Physics - Theory (hep-th) ,Nonperturbative Effect ,Focus (optics) - Abstract
This paper addresses a long standing problem, the counting of the microstates of supersymmetric asymptotically AdS black holes in terms of a holographically dual field theory. We focus on a class of asymptotically AdS$_4$ static black holes preserving two real supercharges which are dual to a topologically twisted deformation of the ABJM theory. We evaluate in the large $N$ limit the topologically twisted index of the ABJM theory and we show that it correctly reproduces the entropy of the AdS$_4$ black holes. An extremization of the index with respect to a set of chemical potentials is required. We interpret it as the selection of the exact R-symmetry of the superconformal quantum mechanics describing the horizon of the black hole., Comment: 35 pages + appendices, 4 figures; v2: refs added
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- View/download PDF
41. Dimensional reduction of BPS attractors in AdS gauged supergravities
- Author
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Kiril Hristov and Hristov, K
- Subjects
High Energy Physics - Theory ,Physics ,Nuclear and High Energy Physics ,Supergravity ,FOS: Physical sciences ,Of the form ,Scalar potential ,AdS-CFT Correspondence ,String theory ,Theoretical physics ,High Energy Physics::Theory ,General Relativity and Quantum Cosmology ,High Energy Physics - Theory (hep-th) ,Dimensional reduction ,Black Holes in String Theory ,Attractor ,Entropy (information theory) ,Embedding ,Supergravity Model - Abstract
We relate across dimensions BPS attractors of black strings and black holes of various topology in gauged supergravities with nontrivial scalar potential. The attractors are of the form AdS$_{2, 3} \times \Sigma^{2, 3}$ in 4, 5, and 6 dimensions, and can be generalized to some higher dimensional analogs. Even though the attractor geometries admit standard Kaluza-Klein and Scherk-Schwarz reductions, their asymptotic AdS spaces in general do not. The resulting lower dimensional objects are black holes with runaway asymptotics in supergravity theories with no maximally symmetric vacua. Such classes of solutions are already known to exist in literature, and results here suggest an interpretation in terms of their higher-dimensional origin that often has a full string theory embedding. In a particular relevant example, the relation between 5d Benini-Bobev black strings arXiv:1302.4451 and a class of 4d Cacciatori-Klemm black holes arXiv:0911.4926 is worked out in full detail, providing a type IIB and dual field theory description of the latter solutions. As a consistency check, the Cardy formula for the field theory is shown to match the Bekenstein-Hawking entropy for horizon topology of any genus., Comment: 17 pages; v2: references added; v3: section 3.4 added, published version
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- View/download PDF
42. A note on the entropy of rotating BPS AdS7 × S4 black holes
- Author
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Kiril Hristov, Alberto Zaffaroni, Seyed Morteza Hosseini, Hosseini, S, Hristov, K, and Zaffaroni, A
- Subjects
Physics ,High Energy Physics - Theory ,Nuclear and High Energy Physics ,010308 nuclear & particles physics ,Extended Supersymmetry ,Astrophysics::High Energy Astrophysical Phenomena ,FOS: Physical sciences ,AdS-CFT Correspondence ,01 natural sciences ,AdS/CFT correspondence ,General Relativity and Quantum Cosmology ,High Energy Physics - Theory (hep-th) ,0103 physical sciences ,Black Holes in String Theory ,lcsh:QC770-798 ,lcsh:Nuclear and particle physics. Atomic energy. Radioactivity ,010306 general physics ,Mathematical physics - Abstract
In this note we show that the entropy of BPS, rotating, electrically charged AdS$_7 \times S^4$ black holes can be obtained by an extremization principle involving a particular combination of anomaly coefficients of the six-dimensional $\mathcal{N} = (2, 0)$ theory. This result extends our previous finding for BPS, rotating AdS$_5 \times S^5$ black holes., 21 pages
- Full Text
- View/download PDF
43. Regenerative endodontic treatment of immature permanent teeth after mechanical instrumentation with XP-Endo Finisher.
- Author
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Hristov K, Doitchinova L, and Gateva N
- Subjects
- Follow-Up Studies, Calcium Hydroxide therapeutic use, Dentition, Permanent, Regenerative Endodontics methods
- Abstract
Introduction: The traditional treatment of immature permanent teeth with necrotic pulp involves creating an apical barrier by using calcium hydroxide or an MTA plug for an extended period of time. A novel therapeutic approach called regenerative endodontic procedures (REP) is used to allow root development to continue., (This is an open access article distributed under the terms of the Creative Commons Attribution License (CC BY 4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.)
- Published
- 2023
- Full Text
- View/download PDF
44. Doppler ultrasound measurements of the blood flow velocity in the fetal heart and aorta in Bulgarian White milk goats.
- Author
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Fasulkov IR, Karadaev M, Vasilev N, Hristov K, and Fedev I
- Subjects
- Animals, Embryo, Mammalian physiology, Aorta physiology, Blood Flow Velocity veterinary, Fetal Heart physiology, Goats physiology, Ultrasonography, Doppler veterinary
- Abstract
The aim of the present study was to determine the parameters characterising the blood flow velocity in the fetal heart and aorta in goats by Doppler ultrasonography. Twenty-four Bulgarian White milk goats, aged 4-6 years, weighing 45-51 kg were used in the study. Doppler ultrasound measurements of the blood flow velocity in fetal heart were done at the end of first, second and third trimesters of pregnancy, and in the fetal aorta - at the end of the second and third trimesters of pregnancy. Ultrasound investigations were carried out by transabdominal approach with linear and convex transducers, with frequency 8.0 MHz. Blood flow parameters that included maximum and minimum systolic velocity, end-diastolic velocity, pulsatility index, resistance index and systolic/diastolic ratio were measured by spectral Doppler ultrasonography. The results showed that the highest maximum systolic velocity in the fetal heart was observed at the end of the first pregnancy trimester. Statistically significantly (p < 0.05) lower values of this parameter were registered in the second and third pregnancy trimesters. A similar tendency was observed for minimum systolic velocity, end-diastolic velocity and systolic/diastolic ratio. The pulsatility index and resistance index had similar values for the three studied periods. Examination of the fetal aorta showed statistically significant differences (p < 0.05) of minimum systolic velocity, end-diastolic velocity, pulsatility and resistance index in the third, compared with the second trimester of pregnancy. The analysis of the results suggested that Doppler ultrasonography can be used to monitor fetal blood flow changes during the various stages of pregnancy., (© 2021 The Authors Veterinary Medicine and Science Published by John Wiley & Sons Ltd.)
- Published
- 2021
- Full Text
- View/download PDF
45. Application of Contemporary Magnifying Methods in the Diagnostics of Occlusal Carious Lesions on First Permanent Molars in Children.
- Author
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Rashkova M, Bogovska-Gigova R, Tankova H, Gateva N, Mitova N, and Hristov K
- Subjects
- Child, Dental Caries pathology, Dentition, Permanent, Humans, Molar pathology, Pediatric Dentistry, Dental Caries diagnostic imaging, Microscopy methods, Molar diagnostic imaging
- Abstract
Introduction: Dental operating microscopes (DOM) enable dentists to examine, with the aid of magnification and photodocumentation in clinical conditions, the occlusal anatomy of newly erupted permanent molars and to detect any early carious lesions more precisely., Aim: To determine the advantages of magnifying technology in detecting early occlusal carious lesions in newly erupted permanent first molars., Materials and Methods: We examined 176 first molars of 44 children divided into two age groups: 7-8 and 9-10 years. The surfaces of each of the teeth were examined after they were cleaned with a brush without paste. The diagnoses were first made using only illumination and a clinical examination. These were followed by a visual examination of the occlusal surface using a DOM at ×8 magnification. A photo of the occlusal surface was then taken with a camera at the respective magnification for the purposes of photodocumentation., Results: This study demonstrated that dental operating microscopes increased by 7% the rate of successful detection of early caries lesions on the occlusal surfaces. There was also a significant increase of the number of diagnosed cavitated caries in the dentine in comparison with those detected with naked eye. Using DOMs in pediatric dentistry facilitates the more detailed and precise diagnosing of early stage carious lesions and/or cavitations in the fissures., Conclusion: The use of a DOM facilitates differential diagnosing between deep fissures and early carious lesions, which is a key point in the assessment of occlusal surfaces of newly erupted permanent molars, necessary for their preventative sealing and micro-invasive treatment., (This is an open access article distributed under the terms of the Creative Commons Attribution License (CC BY 4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.)
- Published
- 2020
- Full Text
- View/download PDF
46. Prevalence of hepatitis C in the adult population of Bulgaria: a pilot study.
- Author
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Sperle I, Nielsen S, Gassowski M, Naneva Z, Perchemlieva T, Amato-Gauci A, An der Heiden M, Bremer V, Golkocheva-Markova E, Hristov K, Kaneva E, Simeonova Y, Tenev T, Varleva T, Duffell E, and Zimmermann R
- Subjects
- Adolescent, Adult, Aged, Aged, 80 and over, Bulgaria epidemiology, Cross-Sectional Studies, Female, Humans, Male, Middle Aged, Pilot Projects, Prevalence, Young Adult, Hepatitis C, Chronic epidemiology
- Abstract
Objective: This study piloted a European technical protocol for conducting chronic hepatitis C prevalence surveys in the general population. The pilot study took place in the Bulgarian city of Stara Zagora in 2018, and results of setting up, conducting and evaluating the survey are presented., Results: A probability-based sample of the general adult population was drawn from the local population registry, stratified by age and sex. A sample size of 999 was calculated, and accounting for 50% non-response, 1998 registered invitation letters were sent. Venous blood samples and questionnaire data were collected by the Regional Health Inspectorate in Stara Zagora. Blood samples were tested for anti-HCV, and if reactive for RNA. 252 (21.6%) of the participants were included in the study. Mean age and sex distribution differed between the participants (55.9 years, 60.3% females) and the total sample (48.9 years, 53.4%). The weighted chronic HCV prevalence among participants was 0.9% [95% CI 0.2-4.2%]. The approach of only sending registered letters contributed to a low response rate, and more efforts are needed to reduce non-response, especially among men and younger age groups. Results of the evaluation were integrated in the final technical protocol.
- Published
- 2020
- Full Text
- View/download PDF
47. Comparative Analysis of Root Dentin Loss when Using Modern Mechanical Cleaning Instruments in Immature Permanent Teeth.
- Author
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Hristov K, Gateva N, Stanimirov P, Ishkitiev N, and Doitchinova L
- Subjects
- Adolescent, Dentin pathology, Female, Humans, In Vitro Techniques, Male, X-Ray Microtomography, Dental Instruments, Dentin diagnostic imaging, Dentition, Permanent, Root Canal Preparation instrumentation
- Abstract
Introduction: The full decontamination and disinfection of the root canal system is essential for the success of regenerative endodontic procedures. The current literature does not have information regarding mechanical cleaning of immature teeth with contemporary endodontic instuments., Aim: To compare the thickness and volume of the dentin removed from the roots of immature teeth after endodontic preparation using XP-endo Finisher, GentleFile Brush and a standard H-file scraping technique through micro-computed tomography., Methods: The study included 51 immature permanent molars. Endodontic access was prepared and without performing preliminary extirpation of the pulp, the teeth were divided into three groups. The first group of teeth were instrumented for two minutes with XP-endo Finisher, the second - two minutes with Gentlefile Brush, in the third group the root canals walls were scraped with a No. 40 H-file. The thickness and the volume of the removed dentin was assessed using micro-CT imaging before and after the use of the instruments., Results: There is no statistically significant difference in the mean values of thickness of dentin removed between the teeth, prepared with XP-endo finisher and Gentlefile Brush. When comparing the mean values of volume of dentin removed between the separate groups, a statistically significant difference was discovered for every compared pair with the highest volume of removed dentin in the group prepared with a hand instrument., Conclusion: The endodontic systems tested when used in immature permanent teeth remove significantly less quantity of hard dental structures compared to a hand file for scraping the root canal., (This is an open access article distributed under the terms of the Creative Commons Attribution License (CC BY 4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.)
- Published
- 2020
- Full Text
- View/download PDF
48. Pathological Changes in Natural Infection of Pheasants with Highly Pathogenic Avian Influenza A (H5N8) in Bulgaria.
- Author
-
Stoimenov GM, Goujgoulova GV, Nikolov B, Hristov K, and Teneva A
- Abstract
Introduction: The study of histopathological changes caused by influenza A (H5N8) viral infection in bird species is essential for the understanding of their role in the spread of this highly infectious virus. However, there are few such studies under natural conditions in minor gallinaceous species. This article describes the pathomorphological findings in Colchis pheasants infected naturally with H5N8 during an epizootic outbreak in Bulgaria., Material and Methods: Samples of internal organs of 10 carcasses were collected for histopathological and immunohistochemical evaluation, virus isolation and identification, and nucleic acid detection., Results: Consistent macroscopic findings were lesions affecting the intestine, heart, lung, and pancreas. Congestion and mononuclear infiltrate were common findings in the small intestine, as were necrosis and lymphoid clusters in the lamina propria of the caeca. Congestion with small focal necrosis and gliosis with multifocal nonpurulent encephalitis were observed in the brain. Myocardial interstitial oedema and degenerative necrobiotic processes were also detected. Immunohistological analysis confirmed systemic infection and revealed influenza virus nucleoprotein in all analysed organs., Conclusion: Variable necrosis was observed in the brain, liver, trachea, heart, small intestine, and caeca. Viral antigen was commonly found in the brain, heart, lung and trachea. Contact with migrating waterfowls was suspected as a reason for the outbreak., Competing Interests: Conflict of Interest Conflict of Interests Statement: The authors declare that there is no conflict of interests regarding the publication of this article., (© 2019 G.M. Stoimenov et al. published by Sciendo.)
- Published
- 2019
- Full Text
- View/download PDF
49. Expression of voltage-gated calcium channels augments cell susceptibility to membrane disruption by nanosecond pulsed electric field.
- Author
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Hristov K, Mangalanathan U, Casciola M, Pakhomova ON, and Pakhomov AG
- Subjects
- Calcium metabolism, Calcium Signaling, Cell Membrane Permeability drug effects, Electroporation methods, HEK293 Cells, Humans, Membrane Potentials, Patch-Clamp Techniques, Calcium Channels metabolism, Cell Membrane metabolism, Electricity, Ion Channel Gating
- Abstract
We compared membrane permeabilization by nanosecond pulsed electric field (nsPEF) in HEK293 cells with and without assembled CaV1.3 L-type voltage-gated calcium channel (VGCC). Individual cells were subjected to one 300-ns pulse at 0 (sham exposure); 1.4; 1.8; or 2.3 kV/cm, and membrane permeabilization was evaluated by measuring whole-cell currents and by optical monitoring of cytosolic Ca
2+ . nsPEF had either no effect (0 and 1.4 kV/cm), or caused a lasting (>80 s) increase in the membrane conductance in about 50% of cells (1.8 kV/cm), or in all cells (2.3 kV/cm). The conductance pathway opened by nsPEF showed strong inward rectification, with maximum conductance increase for the inward current at the most negative membrane potentials. Although these potentials were below the depolarization threshold for VGCC activation, the increase in conductance in cells which expressed VGCC (VGCC+ cells) was about twofold greater than in cells which did not (VGCC- cells). Among VGCC+ cells, the nsPEF-induced increase in membrane conductance showed a positive correlation with the amplitude of VGCC current measured in the same cells prior to nsPEF exposure. These findings demonstrate that the expression of VGCC makes cells more susceptible to membrane permeabilization by nsPEF. Time-lapse imaging of nsPEF-induced Ca2+ transients confirmed permeabilization by a single 300-ns pulse at 1.8 or 2.3 kV/cm, but not at 1.4 kV/cm, and the transients were expectedly larger in VGCC+ cells. However, it remains to be established whether larger transients reflected additional Ca2+ entry through VGCC, or were a result of more severe electropermeabilization of VGCC+ cells., (Copyright © 2018 Elsevier B.V. All rights reserved.)- Published
- 2018
- Full Text
- View/download PDF
50. L-2-oxothiazolidine-4-carboxylate influence on age- and heat exposure-dependent redox changes in rat's blood plasma.
- Author
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Hadzi-Petrushev N, Jankulovski N, Hristov K, and Mladenov M
- Subjects
- Animals, Glutathione blood, Ketones blood, Male, Oxidation-Reduction, Oxidative Stress drug effects, Rats, Rats, Wistar, Sulfhydryl Compounds blood, Hot Temperature, Pyrrolidonecarboxylic Acid pharmacology, Thiazolidines pharmacology
- Abstract
In the present study, we investigated both the age- and heat exposure-related redox changes of blood plasma by analyzing GSH, thiol status and carbonyl groups. Our results clearly indicated that the plasma redox balance shifted toward oxidation during both aging and acute heat exposure. To further confirm this age- and heat exposure-related redox shift, we quantified the changes in thiol content. The total thiol level was found to be significantly decreased in the aged group. A similar pattern can be explained by low levels of serum GSH in old rats compared to young rats. The significance of the present study are the data showing increased oxidative stress in plasma during aging, attributed to a decrease in major antioxidant components in serum. OTC treatment, in relation to C=O regarded as a marker of oxidative damage was probably much more effective in increasing of GSH synthesis than in prevention of protein oxidation.
- Published
- 2011
- Full Text
- View/download PDF
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