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Further to planar single-layer hexagonal structures, GaN and AlN can also form free-standing, single-layer structures constructed from squares and octagons. We performed an extensive analysis of dynamical and thermal stability of these structures in terms of ab initio finite-temperature molecular dynamics and phonon calculations together with the analysis of Raman and infrared active modes. These single-layer square-octagon structures of GaN and AlN display directional mechanical properties and have wide, indirect fundamental band gaps, which are smaller than their hexagonal counterparts. These density functional theory band gaps, however, increase and become wider upon correction. Under uniaxial and biaxial tensile strain, the fundamental band gaps decrease and can be closed. The electronic and magnetic properties of these single-layer structures can be modified by adsorption of various adatoms, or by creating neutral cation-anion vacancies. The single-layer structures attain magnetic moment by selected adatoms and neutral vacancies. In particular, localized gap states are strongly dependent on the type of vacancy. The energetics, binding, and resulting electronic structure of bilayer, trilayer, and three-dimensional (3D) layered structures constructed by stacking the single layers are affected by vertical chemical bonds between adjacent layers. In addition to van der Waals interaction, these weak vertical bonds induce buckling in planar geometry and enhance their binding, leading to the formation of stable 3D layered structures. In this respect, these multilayers are intermediate between van der Waals solids and wurtzite crystals, offering a wide range of tunability. [ABSTRACT FROM AUTHOR]

In-plane composite structures constructed of the stripes or core/shells of single-layer GaN and AlN, which are joined commensurately, display a diversity of electronic properties that can be tuned by the size of their constituents. In heterostructures, the dimensionality of the electrons changes from two dimensional (2D) to one dimensional (1D) upon their confinements in wide constituent stripes, leading to the type-I band alignment and hence multiple quantum well structure in the direct space. The δ doping of one wide stripe by another narrow stripe results in local narrowing or widening of the band gap. A single quantum well structure is acquired from the finite-size AlN-GaN-AlN junctions. In a patterned array of GaN/AlN core/shells, the dimensionality of the electronic states is reduced from two dimensional to zero dimensional, forming multiple quantum dots in large GaN cores, while 2D electrons propagate in multiply connected AlN shell as if they are in a supercrystal. A consistent and detailed discussion of the effects of confinement in momentum and direct spaces is provided. As a result of confinement, the variation of the band gap in the direct space is found to be rather different from the edges of the conduction and valence bands inferred from the band edges of constituent 2D single-layer GaN and AlN. Even if all the results in this study pertain to the free-standing single-layer composite structures, the effects of the different substrates over which these composites can grow are examined in detail. This study unveils the potential of composite structures in designing novel nanomaterials. These predictions are obtained from first-principles calculations based on density functional theory on 2D GaN and AlN compound semiconductors which were synthesized recently. [ABSTRACT FROM AUTHOR]

In this paper we investigated the interaction between a graphene nanoflake anchored to the 2D graphene monolayer. This interaction is attractive but weak and is capable of setting a well defined registry in equilibrium. Rotational and linear displacements from equilibrium registry generate restoring forces, which can be controlled by external agents. Similar flakes can be self-assembled and can also execute simple harmonic motion as if a physical pendulum. Oscillation of a nanoflake about their equilibrium registries resulting in a characteristic libration frequency is predicted. This frequency depends on the size and geometry of the flake. Moreover, the libration frequency, as well as the electronic and magnetic properties of the flake+monolayer systems, can be tuned by a foreign molecule anchored to the flake, by electric charging and applied parallel and perpendicular electric and magnetic fields. When the sliding of the flake is combined with rotation, the friction force can be reduced dramatically. It is surprising that weak interaction can offer such features at nanoscale, which may offer potential applications. Our predictions are obtained by first-principles calculations based on density functional theory. [ABSTRACT FROM AUTHOR]

Three-dimensional (3D) GaN is a III-V compound semiconductor with potential optoelectronic applications. In this paper, starting from 3D GaN in wurtzite and zinc-blende structures, we investigated the mechanical, electronic, and optical properties of the 2D single-layer honeycomb structure of GaN (g-GaN) and its bilayer, trilayer, and multilayer van der Waals solids using density-functional theory. Based on high-temperature ab initio molecular-dynamics calculations, we first showed that g-GaN can remain stable at high temperature. Then we performed a comparative study to reveal how the physical properties vary with dimensionality. While 3D GaN is a direct-band-gap semiconductor, g-GaN in two dimensions has a relatively wider indirect band gap. Moreover, 2D g-GaN displays a higher Poisson ratio and slightly less charge transfer from cation to anion. In two dimensions, the optical-absorption spectra of 3D crystalline phases are modified dramatically, and their absorption onset energy is blueshifted. We also showed that the physical properties predicted for freestanding g-GaN are preserved when g-GaN is grown on metallic as well as semiconducting substrates. In particular, 3D layered blue phosphorus, being nearly lattice-matched to g-GaN, is found to be an excellent substrate for growing g-GaN. Bilayer, trilayer, and van der Waals crystals can be constructed by a special stacking sequence of g-GaN, and they can display electronic and optical properties that can be controlled by the number of g-GaN layers. In particular, their fundamental band gap decreases and changes from indirect to direct with an increasing number of g-GaN layers. [ABSTRACT FROM AUTHOR]

Objective: Because of the immature bone marrow signal in children, assessment of the sacroiliac joint is more difficult than in adults. Aim of this study is to evaluate the efficacy of diffusion-weighted imaging (DWI) in sacroiliac joint magnetic resonance imaging (MRI)., Methods: Sacroiliac joint MRI, including DWI sequences, were evaluated by two pediatric radiologists in 54 patients with sacroiliitis and 85 completely normal controls. In MRI evaluation, subchondral bone marrow edema and contrast enhancement in the sacroiliac joints were considered as active sacroiliitis. Apparent diffusion coefficient (ADC) measurements were made in six areas from each sacroiliac joint. A total of 1668 fields were evaluated retrospectively without their diagnosis being known., Results: When the postcontrast T1W series were referenced, the sensitivity, specificity, positive predictive value, and negative predictive value of short time inversion recovery (STIR) images in the diagnosis of sacroiliitis were 88%, 92%, 83% and 94% respectively, compared to contrast-enhanced images. False positive results in STIR images were observed secondary to the flaring signal in the immature bone marrow. ADC measurements obtained from diffusion-weighted images were recorded in all patients and healthy groups. The ADC values were 1.35x10 -3 mm 2 /s (SD: 0.21) in the areas of sacroiliitis, 0.44x10 -3 mm 2 /s (SD: 0.71) in the normal bone marrow and 0.72x10 -3 mm 2 /s (SD: 0.76) in the immature bone marrow areas., Conclusion: Although STIR studies are an effective sequence in the diagnosis of sacroiliitis, they cause false positive results in immature bone marrow in children in inexperienced hands. DWI is an objective method that prevents errors in the assessment of sacroiliitis by means of ADC measurements in the immature skeleton. In addition, it is a short and effective MRI series that makes important contributions to the diagnosis without the need for contrast-enhanced examinations in children., Competing Interests: No conflict of interest was declared by the authors., (© Copyright 2023 by Istanbul Provincial Directorate of Health.)

Objective: The objective of the study was to describe the findings of pediatric patients diagnosed with COVID-19 in computed tomography (CT) and chest X-ray (CXR) images. Therefore, the aim of this study is to show protecting the children from radiation as much as possible while guiding the diagnosis., Methods: Between March and June 2020, 148 pediatric patients examined who underwent CT due to suspicion of COVID-19. Fifty patients of 148 with normal thorax CT and negative reverse transcription polymerase chain reaction (RT-PCR) were excluded from the study. Of the remaining 98 patients were evaluated retrospectively by two pediatric radiologists with 15 years of experience., Results: The demographic, clinical, and laboratory data were evaluated for 52 RT-PCR-positive patients. CT finding of 23 RT-PCR positive and 12 negative patients was classified. According to our study, unilateral (61-67%), multifocal (50-52%), and peripheral (83-91%) involvement were higher in all groups. Lower lobe involvement was frequently detected (58-65%). The most frequently detected parenchymal lesion was ground-glass opacity followed by consolidated areas accompanying ground-grass opacities. Halo sign and vascular enlargement signs were the common signs of lung lesions (35%). In addition, some rare findings not previously described in this disease in children were mentioned in this study. The clinical course of all our patients was mild and control radiological imaging checked by CXR., Conclusion: Most pediatric patients have a mild course. Hence, a balance between the risk of radiation and necessity for chest CT is very important. Low-dose CT scan is more suitable for pediatric patients but still it should be used cautiously., Competing Interests: Conflict of Interest: No conflict of interest was declared by the authors., (Copyright: © 2021 by Istanbul Northern Anatolian Association of Public Hospitals.)

In this paper we investigate the interaction between a pristine blue phosphorene monolayer and selected organic molecules like amino acids and nucleic acid bases. These molecules are bound to the substrate by a weak van der Waals interaction leading to their physisorption. When isolated, they tend to orient themselves parallel to the surface and are located in flat minima with very low libration frequencies; thus the electronic structures of the substrate and physisorbed molecules are not affected except for relative shifts. Even though the regular self-assembly of these molecules on the pristine blue phosphorene cannot be realized under this weak interaction, only their irregular coating of the substrate can occur due to increased intermolecular coupling. In a solvent like water, the weak binding energy is further decreased. Gold adatoms and gold clusters can form strong chemical bonds with pristine blue phosphorene and modify its electronic and magnetic state depending on the coverage. While full coverage of a blue phosphorene monolayer by gold adatoms leads to instabilities followed by clustering, relatively lower coverage can attribute very interesting magnetic and electronic states, like a spin gapless semiconductor. When bound to the gold clusters already adsorbed on the blue phosphorene monolayer, amino acid and nucleic acid base molecules form relatively strong chemical bonds and hence can be fixed to the surface; they are reoriented to gain self-assembly character and the whole system acquires new functionalities.

Semiconducting selenium and tellurium in their 3D bulk trigonal structures consist of parallel and weakly interacting helical chains of atoms and display a number of peculiarities. We predict that thermal excitations, 2D compressive strain and excess charge of positive and negative polarity mediate metal-insulator transitions by transforming these semiconductors into different metallic crystal structures. When heated to high temperature, or compressed, or charged positively, they change into a simple cubic structure with metallic bands, which is very rare among elemental crystals. When charged negatively, they transform first into body-centered tetragonal and subsequently into the body-centered orthorhombic structures with increasing negative charging. These two new structures stabilized by excess electrons also have overlapping metallic bands and quasi 2D and 1D substructures of lower dimensionality. Since the external charging of crystals can be achieved through their surfaces, the effects of charging on 2D structures of selenium and tellurium are also investigated. Similar structural transformations have been mediated also in 2D nanosheets and free-standing monolayers of these elements. These phase changes assisted by phonons are dynamical, reversible and tunable; the resulting metal-insulator transitions can occur within very short time intervals and may offer important device applications.

Background: The aim of the study was to establish computed tomography (CT) characteristics, distribution and provide normative data about size of normal inguinal lymph nodes in a paediatric population., Materials and Methods: Four hundred eighty-one otherwise healthy children (147 girls, mean age: 8.87, range 0-17 years) underwent pelvic CT in the setting of high-energy trauma were included in the study. Both axial and coronal 1.25-mm reconstructions were evaluated for the presence, location (deep or superficial), number, presence of fat attenuation, and shape of the lymph nodes, short-axis diameter of the biggest lymph node for each of right and left inguinal regions., Results: A total of 7556 lymph nodes were detected in 481 subjects (the mean count of superficial and deep inguinal lymph nodes was 13.35 [range 6-23] and 2.36 [range 0-7] per subject, respectively): 15% (1135/7556) deep located, 85% (6421/7556) superficially located, 86.6% (6547/7556) with fat attenuation, 99.2% (7496/7556) oval in shape, 0.8% (60/7556) spherical. The short-axis diameter of the lymph nodes increased with age. Pearson's correlation coefficient for superficial and deep lymph nodes in boys and girls, respectively: 0.538 (p < 0.001), 0.504 (p < 0.001), 0.452 (p < 0.001) and 0.268 (p < 0.001). The mean maximum short-axis diameters in different age groups and gender varied between 6.33 ± 0.85 mm and 8.68 ± 1.33 mm for superficial, 3.62 ± 1.16 mm and 5.83 ± 1.05 mm for deep inguinal lymph nodes., Conclusions: Inguinal lymph nodes were multiple, commonly contained fat, and were oval in shape. The data determined about inguinal lymph node size in different paediatric age groups may be applicable as normative data in daily clinical CT evaluation practice.

Group-VA elements P, As, Sb, and Bi can construct free-standing, stable zigzag monatomic chain structures, which show unusual properties. They are normally semimetals with bands crossing at the Fermi level, but a very narrow gap opens due to spin-orbit coupling. They attain one quantum of conductance under a small bias potential; Bi, being an exception, attains two quanta of conductance. Finite size chains are magnetic semiconductors; their magnetic moments and the order of spin states show an even-odd disparity depending on the number of chain atoms. Variations of the HOMO-LUMO band gaps depending on the spin polarization and the size of the finite chains offer critical tunability. In the periodic, zigzag compound chains, a small band gap opens at the Fermi level. The mysterious zigzag geometry, cohesion, stability and band order of all these chains are well-explained by a simple bond model. When placed on the parent or other monolayers like graphene, h-BN and GaSe, these chains become weakly bound and construct a 1D metallic channel. The artificial grids or networks of these metallic chains on the insulating substrates can constitute metal-insulator frameworks of desired geometry. The zigzag phosphorene chain, having the highest stability, remains stable even at full coverage of adsorbates like H and OH, whereas other chains dissociate. While P-chains can be synthesized on GaSe and graphene substrates, phosphorene nanoribbons can transform into suspended chains under excessive tensile strain. Additionally, we showed that As, Sb, and Bi zigzag chains are weakly bound to their parent monolayers and remain stable. Nitrogen monatomic chains, on the other hand, are prone to instability. The diverse properties unveiled in this study based on the density functional method offer tunability through electric fields and strain.

Two-dimensional (2D) antimonene, bismuthene, and their binary compound 2D BiSb possess high spin-orbit coupling (SOC) and potential topological insulator properties upon engineering their structural and chemical properties. Based on many-body first-principles calculations, we show that these materials can exhibit isotropic or anisotropic optoelectronic properties depending on their geometry, i.e. buckled (hb) or asymmetrical washboard (aw) phases. SOC significantly alters their optoelectronic properties, which is predominantly evident in 2D bismuthene. hb-antimonene absorbs light in the visible and partially in the ultraviolet regimes, while the absorption band edge for aw-antimonene, hb- and aw-bismuthene is set at the infrared region, absorption being spread as a broadband optical response through the spectral range. An exciton binding with 0.18 eV energy is detected for hb-bismuthene. Due to their broadband optical response, antimonene, bismuthene, and their binary compound offer possibilities towards applications as 2D materials in solar cells, light-emitting devices, photodetectors and light modulation.

A suspended single layer of GaN in a honeycomb structure is stable in a planar geometry. By stacking these GaN layers one can construct bilayers or multilayers, even new three-dimensional (3D) periodic structures. In this study, we clarified how the planar layers are buckled with the onset of vertical Ga-N bonds. Among the four stable phases of bilayer GaN, only one of them maintains the planar geometry, which is bound by weak van der Waals interactions. For the remaining three phases, the layers are buckled with the onset of weak vertical bonds, and attain total energies slightly lower than that of the planar geometry. Structural phase changes, as well as direct-indirect band transitions take place under strain and electrostatic charging. The vertical bonds become shorter in multilayers, and eventually attain the bulk value. Among the stable phases of 3D periodic GaN, only one with a graphite-like structure behaves as a layered, van der Waals solid; whereby others are 3D uniform crystals beyond the van der Waals solid.

We investigated the effects of chemical/substitutional doping, hydrogenation, and anti-site and vacancy defects on the atomic, optoelectronic and magnetic properties of AlN and GaN monolayers. Upon doping of selected atoms, AlN and GaN monolayers can acquire magnetic properties, and their fundamental band gaps are modified by the localized gap states. Spin-polarized gap states broaden into bands at patterned coverage of adatoms, whereby half-metallic or magnetic semiconducting properties can be attained. Specific adatoms adsorbed to Ga atoms break the nearest vertical Ga-N bonds in the GaN bilayer in the heackelite structure and result in changes in the electronic and atomic structure. While adjacent and distant pairs of anion + cation vacancies induce spin polarization with filled and empty gap states, anti-site defects remain nonmagnetic; but both defects induce dramatic changes in the band gap. Fully hydrogenated monolayers are stable only for specific buckled geometries, where one geometry can also lead to an indirect to direct band gap transition. Also, optical activity shifts to the ultra-violet region upon hydrogenation of the monolayers. While H2 and O2 molecules are readily physisorbed on the surfaces of the monolayers with weak van der Waals attraction, they can be dissociated into constituent atoms at the vacancy site of the cation. Our study performed within density functional theory shows that the electronic, magnetic and optical properties of AlN and GaN monolayers can be tuned by doping and point defect formation in order to acquire diverse functionalities.

Objectives: Wilson's disease (WD) is characterized with the accumulation of copper in the liver and brain. The objective of this study is to quantitatively measure the susceptibility changes of basal ganglia and brain stem of pediatric patients with neurological WD using quantitative susceptibility mapping (QSM) in comparison to healthy controls., Methods: Eleven patients with neurological WD (mean age 15 ± 3.3 years, range 10-22 years) and 14 agematched controls were prospectively recruited. Both groups were scanned on a 1.5 Tesla clinical scanner. In addition to T 1 - and T 2 -weighted MR images, a 3D multi-echo spoiled gradient echo (GRE) sequence was acquired and QSM images were derived offline. The quantitative measurement of susceptibility of corpus striatum, thalamus of each hemisphere, midbrain, and pons were assessed with the region of interest analysis on the QSM images. The susceptibility values for the patient and control groups were compared using twosample t-test., Results: One patient with WD had T 1 shortening in the bilateral globus pallidus. Another one had hyperintensity in the bilateral putamen, caudate nuclei, and substantia nigra on T 2 -weighted images. The rest of the patients with WD and all subjects of the control group had no signal abnormalities on conventional MR images. The susceptibility measures of right side of globus pallidus, putamen, thalamus, midbrain, and entire pons were significantly different in patients compared to controls (P < 0.05)., Conclusion: QSM method exhibits increased susceptibility differences of basal ganglia and brain stem in patients with WD that have neurologic impairment even if no signal alteration is detected on T 1 - and T 2 -weighted MR images.

Purpose: To prospectively compare the diagnostic capabilities of quantitative susceptibility mapping (QSM) with those of phase images of susceptibility-weighted imaging (SWI) in the detection and differentiation of intracranial calcification and hemorrhage in pediatric patients., Method: Sixteen pediatric patients (9 girls, 7 boys) with a mean age of 9.4±6.3 (SD) years (range, 6 days-15 years) were included. Fifty-nine calcifications and 31 hemorrhages were detected. Sensitivities and specificities of the two magnetic resonance (MR) imaging techniques were calculated and compared using McNemar test., Results: QSM had a sensitivity of 84.7% and specificity of 100% for the detection of calcification. SWI phase images had a sensitivity of 49.1% and specificity of 100%. For the detection of hemorrhage, QSM had a sensitivity of 90.3% and a specificity of 98.3% whereas SWI phase images yielded a sensitivity of 64.5% and specificity of 96.6%. Overall, QSM displayed significantly better sensitivity than SWI phase images in identification of calcification and hemorrhage (P<0.05)., Conclusion: QSM is more reliable than SWI phase images in the identification of intracranial calcification and hemorrhage in pediatric patients using MR imaging., (Copyright © 2017 Editions françaises de radiologie. Published by Elsevier Masson SAS. All rights reserved.)

Purpose: To investigate the contribution of preoperative apparent diffusion coefficient (ADC) values in the differential diagnosis of pediatric posterior fossa tumors., Methods: Forty-two pediatric patients (mean age 7.76 ± 4.58 years) with intra-axial tumors in the infra-tentorial region underwent magnetic resonance imaging. ADC measurement was performed using regions of interest, obtained from the solid component of the mass lesions. ADC ratios were calculated by dividing the ADC values from the mass lesions by the ADC values from normal cerebellar parenchyma. Lesions were categorized as juvenile pilocytic astrocytoma (JPA), ependymoma and medulloblastoma based on histopathological diagnosis. ADC values of the lesions and histopathological diagnoses were statistically correlated., Results: Histopathological diagnosis showed that 14 lesions were JPA, 10 were ependymoma; 18 were medulloblastoma. Both ADC values and ADC ratios were significantly correlated with tumor types (p <0.05). Astrocytoma was distinguished from ependymoma with sensitivity 85.7% and specificity 90% using an ADC ratio ≥1.7 and medulloblastoma was distinguished from ependymoma with sensitivity 100% and specificity 88.89% using an ADC ratio ≤1.18., Conclusion: Preoperative ADC values could differentiate the main histological subtypes of pediatric posterior fossa tumors with high sensitivity and specificity.

Background: Familial hemophagocytic lymphohistiocytosis (HLH) is a fatal disease affecting infants and very young children. Central nervous system involvement of HLH can cause catastrophic results., Method: We present a case with cranial involvement of familial HLH type 4 who showed diffuse infiltration of white matter complicated with intracranial thrombosis. A 5-year-old girl from a consanguineous couple presented with fever and pancytopenia, and was referred to our hematology unit. Examination revealed fever, lymphadenopathy, and hepatosplenomegaly. Ultrasound examination revealed hepatosplenomegaly and free intra-abdominal fluid. HLH was revealed on bone marrow aspiration biopsy. Defective natural killer and T lymphocyte cytotoxicity using degranulation tests was determined. In the genetic analysis, syntaxin gene mutation was found. On T2-weighted and T2-fluid-attenuated inversion recovery magnetic resonance imaging (MRI), diffuse hyperintense signal changes of cerebral white matter, indicating white matter demyelination, were observed. A second brain MRI showed an acute infarct involving the left temporooccipital region. Immunosuppressive therapy according to the HLH 2004 protocol was started. The infarct resolved but white matter lesions were stable on the brain MRI that was performed 1 month later. Brain MRI taken 4 months after the first examination showed stable cerebral white matter lesions, but hyperintense signal changes appeared in the cerebellar white matter and were regarded as progression. The patient died because of infection despite immunosuppressive therapy., Conclusions: Physicians managing patients with HLH must be vigilant about the possibility of central nervous system involvement including stroke.

The orbital pathologies commonly detected during the childhood period substantially differ from the lesions that arise in adult orbit. The advance in imaging modalities including computed tomography (CT) and particularly magnetic resonance imaging (MRI) might enable the radiologists and clinicians who would be involved in either medical or surgical care of orbital pathologies, to confidently establish a definite diagnosis prior to histopathologic examination. The purpose of this pictorial assay is to present relatively common paediatric orbital pathologies with regard to CT and MRI findings.

Neuroblastoma is the most common extracranial solid tumor of childhood originating from sympathetic nervous system cells. Neuroblastoma has also been diagnosed in conjunction with other congenital conditions such as Hirschsprung's disease, congenital hypoventilation disorder, and neurofibromatosis type 1. Wolf-Hirschhorn syndrome is a congenital disorder caused by microdeletion of short arm of chromosome 4 encoding MSX1 gene with characteristic facial features. We describe a child with dysmorphic features, developmental delay, mental retardation who developed neuroblastoma at 2 years of age and cytogenetic analysis of blood lymphocytes revealed an interstitial deletion of 4p(15,2). To best our knowledge, this report is the first report of neuroblastoma in a child with Wolf-Hirschhorn syndrome; and the reported association may be an important clue for oncological follow-up of patients with Wolf-Hirschhorn syndrome.

Germanene, a graphene-like single-layer structure of Ge, has been shown to be stable and recently grown on Pt and Au substrates. We show that a Ge adatom adsorbed on germanene pushes down the host Ge atom underneath and forms a dumbbell structure. This exothermic process occurs spontaneously. The attractive dumbbell-dumbbell interaction favors high coverage of dumbbells. This Letter heralds stable new phases of germanene, which are constructed from periodically repeating coverage of dumbbell structures and display diversity of electronic and magnetic properties.

Silica or SiO(2), the main constituent of Earth's rocks has several 3D complex crystalline and amorphous phases, but it does not have a graphitelike layered structure in 3D. Our theoretical analysis and numerical calculations from the first principles predict a single-layer honeycomblike allotrope, hα silica, which can be viewed to be derived from the oxidation of silicene and it has intriguing atomic structure with reentrant bond angles in hexagons. It is a wide band gap semiconductor, which attains remarkable electromechanical properties showing geometrical changes under an external electric field. In particular, it is an auxetic metamaterial with a negative Poisson's ratio and has a high piezoelectric coefficient. While it can form stable bilayer and multilayer structures, its nanoribbons can show metallic or semiconducting behavior depending on their chirality. Coverage of dangling Si orbitals by foreign adatoms can attribute new functionalities to hα silica. In particular, Si(2)O(5), where Si atoms are saturated by oxygen atoms from top and bottom sides alternatingly can undergo a structural transformation to make silicatene, another stable, single layer structure of silica.

Purpose: The purpose of this study was to investigate whether the sonographic echogenicity of embryos is associated with cardiac activity in utero., Methods: The present study reviewed a total of 164 embryos having a gestational age between 6 and 8 weeks. These embryos were examined by transvaginal ultrasonography and a comparison of their echogenicity was made with respect to those of the placenta and the myometrium. Grade II embryos were less echogenic than the placenta or had similar echogenicity with the myometrium, whereas grade I embryos shared the same echogenicity as the placenta. In contrast, grade III embryos were less echogenic than the myometrium., Results: Most of the embryos with cardiac activity were detected to have grade II echogenicity (78/130, 60.0%), whereas the remaining embryos had grade I echogenicity (52/130, 40.0%). In contrast, most of the embryos without cardiac activity had grade III echogenicity (20/34, 58.8%), whereas the remaining embryos had either grade II (8/34, 23.5%) or grade I (6/34, 17.7%) echogenicity., Conclusions: Decreased echogenicity of embryos on grayscale ultrasound in the early first trimester is correlated with an absence of cardiac activity., (Copyright © 2012 Wiley Periodicals, Inc.)

Ascorbic acid oxidase (AAO) is a plant blue-copper protein catalyzing dioxygen reduction to water using ascorbic acid as the electron donor. In spite of extensive molecular characterization the physiological role of AAO is still uncertain. Abundant mRNA, protein and activity of AAO were observed in illuminated leaves of Cucurbita pepo. AAO activity was found to be proportional to light intensity. The light effect was rapidly reversed in dark and activity remained low throughout the dark period. Activity was elicited in dark by increased oxygen concentration. AAO activity increased in the facultative CAM Kalanchoë blossfeldiana upon induction of the CAM cycle and decreased during germination of C. pepo and Zea mays under hypoxic conditions. These results strongly suggest that AAO activity could be part of a dynamic system for oxygen management in plants.

To understand the function of ascorbic acid (ASC) in root development, the distribution of ASC, ASC oxidase, and glutathione (GSH) were investigated in cells and tissues of the root apex of Cucubita maxima. ASC was regularly distributed in the cytosol of almost all root cells, with the exception of quiescent centre (QC) cells. ASC also occurred at the surface of the nuclear membrane and correspondingly in the nucleoli. No ASC could be observed in vacuoles. ASC oxidase was detected by immunolocalization mainly in cell walls and vacuoles. This enzyme was particularly abundant in the QC and in differentiating vascular tissues and was absent in lateral root primordia. Administration of the ASC precursor L-galactono-gamma-lactone markedly increased ASC content in all root cells, including the QC. Root treatment with the ASC oxidized product, dehydroascorbic acid (DHA), also increased ASC content, but caused ASC accumulation only in peripheral tissues, where DHA was apparently reduced at the expense of GSH. The different pattern of distribution of ASC in different tissues and cell compartments reflects its possible role in cell metabolism and root morphogenesis.

First-principles calculations show that monatomic strings of carbon have high cohesive energy and axial strength, and exhibit stability even at high temperatures. Because of their flexibility and reactivity, carbon chains are suitable for structural and chemical functionalizations; they also form stable ring, helix, grid, and network structures. Analysis of electronic conductance of various infinite, finite, and doped string structures reveal fundamental and technologically interesting features. Changes in doping and geometry give rise to dramatic variations in conductance. In even-numbered linear chains, strain induces a substantial decrease of conductance. The double covalent bonding of carbon atoms underlies their unusual chemical, mechanical, and transport properties.