Search

Anticlastic deformation (AD) is an established mechanical property of isotropic solid bodies, which has been recently used to steer particle beams through channeling in Si crystals. An analysis of AD in an anisotropic material, such as Si, has been worked out with particular emphasis to the cases used in channeling experiments. Both a theoretical model and finite element simulations were developed and compared to experimental data achieved by optical profilometry on bent Si crystals. A quantifier of the extent of AD, namely the ratio between primary and secondary curvature radii, has been found to be orientation dependent and determined analytically. The realistic case of crystal bending by a mechanical holder has been studied for applications. We addressed the case of the holder with a crystal at the energy currently under operation in the CERN super proton synchrotron and its possible extension to higher energy cases such as for the large hadron collider. Anisotropy-driven torsion of the crystal was investigated, determining a limitation to the portion of the crystal suitable for channeling. The geometry of the jaws clamping the crystal was considered too. [ABSTRACT FROM AUTHOR]

A semiclassical model for Schottky contacts to be applied to nanosized polycrystalline n-type semiconductors was developed. To this purpose we determined the density of surface states as a function of the mean grain radius, which establishes the Schottky barrier height. The intergranular potential shape was investigated in depletion approximation under spherical geometry and a critical revision of this method was proposed. The model was then extended to also include nanostructured materials, which could not be considered in the previous approach. Thus we were able to explain the flattening of the band bending and the decrease in the surface state density, which are experimentally observed when the granulometry is very fine. [ABSTRACT FROM AUTHOR]

Reports that structural characterization of nanosized W-Ti-O rf magnetron-sputtered films was performed by means of electron microscopy techniques and Rutherford backscattering spectroscopy. Evolution of the films; Electron microscopy investigation; Film characterization; Microstructural characterization.

Abstract: Pathogens of medical or veterinary significance that are transmitted by mosquitoes (Diptera: Culicidae) are (re‐)emerging in Europe [e.g. West Nile virus (WNV), Dirofilaria nematodes]. Little is known about the spatiotemporal abundances of mosquito species in Switzerland. Therefore, mosquito population dynamics were investigated, focusing on areas of risk for sylvatic or synanthropic transmission, such as natural sites and suburban sites on either side of the Alpine crest. Repeated collections were made using Centers for Disease Control (CDC) traps, juvenile sampling and ovitrapping. A total of 122 831 mosquito specimens of 21 taxa were identified. Levels of mosquito species richness were similar at suburban sites and in natural zones in Switzerland. Mosquito abundances and seasonality were analysed with generalized linear mixed models based on 382 CDC trap samples (29 454 females) and revealed Aedes annulipes/cantans, Aedes geniculatus, Aedes japonicus, Aedes sticticus, Aedes vexans, Coquillettidia richiardii and Culex pipiens/torrentium as the dominant species overall. Abundances of these species were season‐dependent in most cases. There was an effect of site with regard to abundance (higher in natural zones), but not with respect to seasonality. Together with data on vector competence and the host preferences of different species, the present data contribute to assessments of risk for pathogen transmission. For example, both natural and suburban environments seem feasible as sites for amplification cycles of WNV and transmission to mammals. [ABSTRACT FROM AUTHOR]

A bent lithium niobate strip was exposed to a 400-GeV/c proton beam at the external lines of CERN Super Proton Synchrotron to probe its capabilities versus coherent interactions of the particles with the crystal such as channeling and volume reflection. Lithium niobate (LiNbO3) exhibits an interplanar electric field comparable to that of Silicon (Si) and remarkable piezoelectric properties, which could be exploited for the realization of piezo-actuated devices for the control of high-energy particle beams. In contrast to Si and germanium (Ge), LiNbO3 shows an intriguing effect; in spite of a low channeling efficiency (3%), the volume reflection maintains a high deflection efficiency (83%). Such discrepancy was ascribed to the high concentration (104 per cm2) of dislocations in our sample, which was obtained from a commercial wafer. Indeed, it has been theoretically shown that a channeling efficiency comparable with that of Si or Ge would be attained with a crystal at low defect concentration (less than ten per cm2). To better understand the role of dislocations on volume reflection, we have worked out computer simulation via dynecharm++ Monte Carlo code to study the effect of dislocations on volume reflection. The results of the simulations agree with experimental records, demonstrating that volume reflection is more robust than channeling in the presence of dislocations. [ABSTRACT FROM AUTHOR]

Abstract: Membranes of micrometer lateral sizes and nanometer thickness are nowadays routinely fabricated through silicon micromachining processes, while more difficult is the fabrication of large areas membranes. In this paper we describe a method for fabrication of large area nanothickness silicon crystalline membranes starting from a SIMOX wafer. The realized structures have been characterized by means of high resolution X-ray diffraction and planar channeling of a 2MeV proton beam. This last analyses demonstrates a very interesting phenomenon: As the beam direction is inclined by less than the planar channelling critical angle with respect to the crystal planes, channeled particles undergo half a “channeling oscillation” and exit the crystal with reversed transverse momenta, i.e., the protons trajectories are ‘‘mirrored’’ by the crystal planes. Over-barrier particles are deflected of a minor extent in the opposite direction with respect to the “mirroring” direction. Observation of such effects not only proves the high crystalline quality of the Si membrane, but open new ways to manipulate high energy charged particle beams through crystals. [Copyright &y& Elsevier]

Abstract: Sensing of typical gaseous pollutants and malodors as a result of decomposition of organic compounds via chemoresistive gas sensors has been addressed. Screen-printed films of a solid solution of mixed Sn and Ti oxides, of mixed W and Sn oxides, and ZnO have been selected for the purpose. We demonstrated that the choice of these films for this specific use leads to an improvement in selective detection of such gases under either dry or wet condition. An array of such sensors is shown to be suitable for implementation of deconvolution algorithms because it makes it easier the concentration data processing. [Copyright &y& Elsevier]

The interaction of a 2 MeV proton beam with an ultrathin unbent Si crystal was studied through simulation and experiment. Crystal thickness along the beam was set at 92 nm, i.e., at half the oscillation wavelength of the protons in the crystal under planar channeling condition. As the nominal beam direction is inclined by less than the critical angle for planar channeling with respect to the crystal planes, underbarrier particles undergo half an oscillation and exit the crystal with the reversal of the transverse momenta; i.e., the protons are "mirrored" by the crystal planes. Over-barrier particles suffer deflection, too, to a direction opposite that of mirroring with a dynamics similar to that of volume reflection in a bent crystal. On the strength of such coherent interactions, charged particle beams can be efficiently steered through an ultrathin unbent crystal by the same physical processes as for thicker bent crystals. [ABSTRACT FROM AUTHOR]

Abstract: In the present work a technique to impart a controlled deformation to a substrate through deposition of a thin film is shown. Such a technique allows film–substrate systems to be tailored with a desired shape for various applications. An analytical model has been applied to calculate the displacements and stresses of a patterned crystalline substrate. Analytical results have also been validated via Finite Element simulations. Si substrates have been patterned with Si3N4 and measurements of the transverse displacement were found to agree with the theoretical predictions. [Copyright &y& Elsevier]

Aim: To develop a rapid real-time PCR method for the specific detection and quantification of Bacillus thuringiensis var. israelensis (Bti) spores present in the environment. Methods and Results: Seven soil samples as well as one sediment sample obtained from various regions of Switzerland and characterized by different granulometry, pH values, organic matter and carbonate content were artificially inoculated with known amounts of Bti spores. After DNA extraction, DNA templates were amplified using TaqMan real-time PCR targeting the cry4Aa and cry4Ba plasmid genes encoding two insecticidal toxins (δ-endotoxins), and quantitative standard curves were created for each sample. Physicochemical characteristics of the samples tested did not influence DNA extraction efficiency. Real-time PCR inhibition because of the presence of co-extracted humic substances from the soil was observed only for undiluted DNA extracts from samples with very high organic matter content (68%). The developed real-time PCR system proved to be sensitive, detecting down to 1 × 103 Bti spores per g soil. One-way analysis of variance confirmed the accuracy of the method. Conclusions: Direct extraction of DNA from environmental samples without culturing, followed by a specific real-time PCR allowed for a fast and reliable identification and quantification of Bti spores in soil and sediment. Significance and Impact of the Study: The developed real-time PCR system can be used as a tool for ecological surveys of areas where treatments with Bti are carried out. [ABSTRACT FROM AUTHOR]

Abstract: Sensing of volatile alkanes via chemoresistive gas sensors has been addressed. Screen-printed films of Au- and Pd-added SnO2 and a solid solution of mixed Sn and Ti oxides have been selected for the purpose. We demonstrate that the films sensitively detect 200ppm of such gases, a value which is by far lower than their alarm limits. Information about the working mechanism of chemical reactions at surface has been discussed. [Copyright &y& Elsevier]

Abstract: The growing interest on micro-beams in recent years and the combined development of channeling technology in high-energy physics have opened the way to new concepts for micro-beams devices. Silicon micromachining technology is here applied to manufacture micro-collimators in inexpensive and feasible ways. Both dry and wet etchings can be employed for the purpose, though the latter technique appears to be cheaper and easier. Two designs for micro-collimator devices have been considered and preliminary samples have been produced accordingly. [Copyright &y& Elsevier]

Abstract: The selective sublimation processing (SSP) is a useful and easy method for production of semiconducting thin films via reactive sputtering for gas sensing. We have investigated the mechanism of film growth and processing for an insight into the main parameters that control the preparation methodology. A model based on diffusion equation, in the framework of a linear theory, has been proposed and compared to experimental evidences. Rutherford backscattering spectrometry has been extensively used as a tool for determination of concentration profiles in the layers. The model allowed a deeper understanding of film preparation with a physical description of the processes involved, which would open up the design of innovative nanostructured materials that rely on SSP. Titania thin films produced by this methodology and proved capable of sensing target gases of interest for many applications. [Copyright &y& Elsevier]

Abstract: In the last years, the research on channeling of relativistic particles has progressed considerably. A significant contribution has been provided by the development of techniques for quality improvement of the crystals. In particular, a planar etching of the surfaces of the silicon crystals proved useful to remove the superficial layer, which is a region very rich in imperfections, in turn leading to greater channeling efficiency. Micro-fabrication techniques, borrowed from silicon technology, may also be useful: micro-indentation and deposition of tensile or compressive layers onto silicon samples allow one to impart an even curvature to the samples. In this way, different topologies may be envisaged, such as a bent crystal for deflection of protons and ions or an undulator to force coherent oscillations of positrons and electrons. [Copyright &y& Elsevier]

Different synthetical routes involving several solvents for obtaining WO3 powders, suitable for gas sensing have been studied. Aqueous and alcoholic solvents proved to be the most promising media to grow nanometric particles. Among these, a modified sol–gel route that involves ethanol and a di-chetone, highlighted a more homogeneous grain-size distribution. The structure and morphology evolution of pure WO3 powders with time and annealing temperature have been studied. The study of the energy barrier and conductance versus temperature allows to understand the reason for the high response of WO3 to oxidising gases and its lack of sensitivity to reducing agents. Films of WO3 responded to NO2, sensing as low a gas concentration as 200 ppb. [Copyright &y& Elsevier]

Nowadays, monitoring landfill produced gases (LFGs) is a major task for environmental safety of the areas neighboring garbage dumps. The authors have explored a novel approach to this problem. We have tested solid-state chemoresistive gas sensors to detect typical complex organic gases produced by landfill, i.e., carbon sulfide, methyl sulfide and xylene. We have prepared TiO2:Mo, MoO3:Ti, TiO+WO3 and TiO:W mixed-oxides thin films deposited by reactive sputtering and then processed through the selective sublimation technique. The layers gave remarkable response towards carbon disulfide and xylene below the attention level for these gases. [Copyright &y& Elsevier]

We report in our research on semiconductor-based sensing layers deposited via thick-film technique. Particular focus was devoted to achieve nanosized films through proper processing and to study their morphological and structural features. Nanosized powders were prepared by sol–gel method or laser-assisted spray pyrolysis. We also considered some techniques to maintain the stability of a nanostructure for long-term usage of the sensing layers. We detailed the preparation of screen printing pastes suitable for gas sensing application. Implementation of the sensing film on a low-power-consumption micromachined hotplate has also been addressed. The performance of such devices is presented and compared to that of conventional units. [Copyright &y& Elsevier]

Abstract: Modeling of the electron charge distribution for very fine nanograins (≈1nm) has been addressed via a semi-classical method such as the Thomas–Fermi approximation. This method takes into account quantum effects of electron confinement within a nanograin and allows one to calculate the height of the inter-grain energy barrier, which is a physical quantity that determines the conductive properties of semiconductor metal-oxides. Comparison with non-quantum models and with experimental measurements is given. [Copyright &y& Elsevier]

The new generation of hadron machines may profitably take advantage of channeling for steering and collimation of high-energy particle beams. In that case, the requirements on the quality of the crystal surface are rather stringent in terms of both lattice perfection and roughness. Here, the authors show the structural and morphological characterizations of crystals fabricated through a method to achieve a surface that fulfills all needed specifications for application in hadron machines. [ABSTRACT FROM AUTHOR]

A crystalline undulator consists of a crystal with a periodic deformation in which channeled particles undergo oscillations and emit coherent undulator radiation. Patterning by an alternate series of tensile Si3N4 strips on a Si crystal is shown to be a tractable method to construct a crystalline undulator. The method allows periodic deformation of the crystal with the parameters suitable for implementation of a crystalline undulator. The resulting periodic deformation is present in the bulk of the Si crystal with an essentially uniform amplitude, making the entire volume of the crystal available for channeling and in turn for emission of undulator radiation. [ABSTRACT FROM AUTHOR]

The height of the intergrain energy barrier plays a key role in the determination of the conductive properties of semiconducting nanograins. In the limit of very-fine nanograins (<1 nm), quantum effects start being relevant in the determination of physical properties. The authors approached the problem in a semiclassical method such as the Thomas-Fermi equation. Its predictions appear to be consistent with experimental evidence. [ABSTRACT FROM AUTHOR]

We present the calibration and data analysis of BULLKID, a cryogenic, low threshold particle detector for searches of low mass dark matter candidates and coherent neutrino on nucleus scattering (CE ν NS) events. The BULLKID detector is an array of 60 cubic particle absorbers made out of 0.34 g of silicon per cube, each one sensed by a kinetic inductance detector (KID). This paper describes the energy calibration of the detector as well as an evaluation of the background rate of the device when operated in an above-ground unshielded environment. By performing coincidence cuts on a cluster of 3x3 dice, the background rejection power of the design is demonstrated, allowing reach to a flat background down to a threshold of 160 eV. [ABSTRACT FROM AUTHOR]

We present the first continuous operation in a surface lab of BULLKID, a detector for searches of light Dark Matter and precision measurements of the coherent and elastic neutrino-nucleus scattering. The detector consists of an array of 60 cubic silicon particle absorbers of 0.34 g each, sensed by cryogenic kinetic inductance detectors. The data presented focusses on one of the central elements of the array and on its surrounding elements used as veto. The energy spectrum resulting from an exposure of 39 h to ambient backgrounds, obtained without radiation shields, is flat at the level of (2.0 ± 0.1 stat. ± 0.2 syst.) × 10 6 counts/keV kg days down to the energy threshold of 160 ± 13 eV. The data analysis demonstrates the unique capability of rejecting backgrounds generated from interactions in other sites of the array, stemming from the segmented and monolithic structure of the detector. [ABSTRACT FROM AUTHOR]

Epidemics of mosquito‐borne diseases such as chikungunya and dengue fever are becoming more frequent around the world. In Switzerland, autochthonous cases have not been reported so far, although the presence of the vector Aedes albopictus in urban areas of southern Switzerland increases the risk of indigenous transmissions subsequent to imported cases. In 2018, the potential risk of an outbreak of arboviral diseases was assessed in five municipalities of southern Switzerland. The population abundance of Ae. albopictus was evaluated during the mosquito active season by the mean number of Ae. albopictus bites per day per person (estimated using the human landing collection method) and the risk of outbreak in the case of the introduction of chikungunya, dengue or Zika viruses was estimated. In the five localities investigated, no epidemic risk appeared to be present for any of the arboviruses taken into consideration in the initial months (i.e. mid‐May to end of July) of Ae. albopictus activity. In the case of the introduction of chikungunya (mutated or not), dengue (serotype 1) or Zika (African lineage) viruses during mid‐end August, an epidemic could have occurred in all the municipalities investigated. In mid‐end September, the introduction of same arboviruses could have led to an epidemic in three of the five municipalities investigated. [ABSTRACT FROM AUTHOR]

Measures the amount of cesium (Cs) on the surface of gallium arsenide (GaAs) photocathode activated in negative electron affinity conditions. Use of Rutherford backscattering spectroscopy; Absence of Cs desorption from the GaAs surface; Reactivation of photocathode surface through Cs feeding.

For applications in high energy particles accelerators, such as the crystal-assisted beam collimation, several strip crystals exploiting anticlastic curvature were produced in the last decade at the Sensor and Semiconductor Laboratory (SSL) of Ferrara by means of revisited techniques for silicon micromachining, such as photolitography and wet etching. Those techniques were recently enhanced by introducing a further treatment called Magnetorheological Finishing (MRF), which allowed to fabricate crystals with ultraflat surface and miscut very close to zero. The technology of the mechanical devices used to hold and bend crystals has been also improved by employing a titanium alloy to realize the holders. Characterization method were also improved: the usage of a high resolution X-rays diffractometer was introduced to directly measure crystal bending and torsion. Accuracy of the diffractometer was furtherly enhanced with an autocollimator, which found an important application in miscut characterization. A new infrared light interferometer was used to map the thickness of the starting swafers with sub-micrometric precision, as well as to measure the length along the beam of the strips. Crystals were characterized at the H8 external lines of CERN-SPS with various hundreds-GeV ion beams, which gave results in agreement with the precharacterization performed at SSL. One strip was selected among the crystals to be installed in the LHC beam pipe during the Long Shutdown 1 in 2014. These crystals were very recently tested in a crystal-assisted collimation experiment with a 6.5 TeV proton beam, resulting in the first observation of channeling at this record energy, being also the first observation of channeling of the beam circulating in the LHC. [ABSTRACT FROM AUTHOR]

We have observed a significant enhancement in the energy deposition by 25– 100 GeV photons in a 1 cm thick tungsten crystal oriented along its ⟨ 111 ⟩ lattice axes. At 100 GeV , this enhancement, with respect to the value observed without axial alignment, is more than twofold. This effect, together with the measured huge increase in secondary particle generation is ascribed to the acceleration of the electromagnetic shower development by the strong axial electric field. The experimental results have been critically compared with a newly developed Monte Carlo adapted for use with crystals of multi- X 0 thickness. The results presented in this paper may prove to be of significant interest for the development of high-performance photon absorbers and highly compact electromagnetic calorimeters and beam dumps for use at the energy and intensity frontiers. [ABSTRACT FROM AUTHOR]

Coherent neutrino-nucleus scattering is a promising new tool in the toolbox of electroweak precision measurements at low q-transfer. It will enable precise measurements of standard model (SM) physics like the running of the Weinberg angle but also the search for new physics beyond the SM like sterile neutrinos. The Nucleus experiment aims at the first detection of fully coherent neutrino-nucleus scattering at the Chooz power plant in France, using its two 4GWth reactor cores as high-intensity source for anti-neutrinos. For this endeavour a new experimental site, the Very Near Site (VNS), with a shallow rock overburden of ≈ 3 m w.e. is under development. To be competitive in this challenging environment, Nucleus developed the novel concept of fiducialised cryogenic bolometers based on CaWO 4 monocrystals operated at O (10 mK). The signature of a coherent neutrino-nucleus scattering is a nuclear recoil at the 10 eV-scale. Currently, Nucleus is preparing its first phase with 10 g of target mass at the VNS. In this contribution, we will first introduce Nucleus, report its current state and give an outlook to its future. [ABSTRACT FROM AUTHOR]

We introduce BULLKID, a phonon detector consisting of an array of dices acting as particle absorbers sensed by multiplexed Kinetic Inductance Detectors (KIDs). The dices are carved in a thick crystalline wafer and form a monolithic structure. The carvings leave a thin common disk intact in the wafer, acting both as holder for the dices and as substrate for the KID lithography. The prototype presented consists of an array of 64 dices of 5.4 × 5.4 × 5 mm3 carved in a 3˝ diameter, 5 mm thick silicon wafer, with a common disk of 0.5 mm thick, hosting a 60 nm patterned aluminum layer. The resulting array is highly segmented but avoids the use of dedicated holding structures for each unit. Despite the fact that the uniformity of the KID electrical response across the array needs optimization, the operation of eight units with similar features shows, on average, a baseline energy resolution of 26 ± 7 eV. This makes it a suitable detector for low-energy processes such as direct interactions of dark matter and coherent elastic neutrino-nucleus scattering. [ABSTRACT FROM AUTHOR]

An intense positron sources is a demanding element in the design of future lepton colliders. A crystal-based hybrid positron source could be an alternative to a more conventional scheme based on the electron conversion into positron in a thick amorphous target. The conceptual idea of the hybrid source is to have two separate objects, a photon radiator and a photon-to-positron converter target. In such a scheme an electron beam crosses a thin axially oriented crystal with the emission of a channeling radiation, characterized by a considerably larger amount of photons if compared to Bremsstrahlung. The net result is an increase in the number of produced positrons at the converter target. In this paper we present the results of a beam test conducted at the DESY TB 21 with 5.6 GeV electron beam and a crystalline tungsten radiator. Experimental data clearly highlight an increased production of photons and they are critically compared with the outcomes of novel method to simulate the number of radiated photons, showing a very good agreement. Strong of this, the developed simulation tool has been exploited to design a simple scheme for a positron source based on oriented crystal, demonstrating the advantages in terms of reduction of both deposited energy and the peak energy deposition density if compared to conventional sources. The presented work opens the way for a realistic and detailed design of a hybrid crystal-based positron source for future lepton colliders. [ABSTRACT FROM AUTHOR]

Crystals with small thickness along the beam exhibit top performance for steering particle beams through planar channeling. For such crystals, the effect of nuclear dechanneling plays an important role because it affects their efficiency. We addressed the problem through experimental work carried out with 400 GeV/c protons at fixed-target facilities of CERN-SPS. The dependence of efficiency vs. curvature radius has been investigated and compared favourably to the results of modeling. A realistic estimate of the performance of a crystal designed for LHC energy including nuclear dechanneling has been achieved. [ABSTRACT FROM AUTHOR]

The radiation emitted by 120 GeV/c electrons traversing a single bent crystal under multiple volume reflection orientation is investigated. Multiple volume reflection in one crystal occurs as a charged particle impacts on a bent crystal at several axial channeling angles with respect to a crystal axis. The resulting energy-loss spectrum of electrons was very intense over the full energy range up to the nominal energy of the beam. As compared to the radiation emission by an individual volume reflection, the energy-loss spectrum is more intense and peaks at an energy 3 times greater. Experimental results are compared to a theoretical approach based on the direct integration of the quasiclassical Baier and Katkov formula. In this way, it is possible to determine the mean number of photons emitted by each electron and, thus, to extract the single-photon spectrum, which is broad and intense. The soft part of the radiation spectrum is due to the contribution of coherent interaction between electrons and several reflecting planes intersecting the same crystal axis, whereas the hard part is mainly connected to coherent bremsstrahlung induced by correlated scattering of electrons by atomic strings (string of strings scattering and radiation). The radiation generation by multiple volume reflection takes place over a broad angular range of the incident beam with respect to coherent bremsstrahlung and channeling radiation in straight crystals. Therefore, this type of radiation can be exploited for applications, such as beam dump and collimation devices for future linear colliders. [ABSTRACT FROM AUTHOR]

A proof-of-principle experimental setup for the extraction of 6 GeV electrons from the DESY II Booster Synchrotron using the channeling effect in a bent crystal is elaborated. Various aspects of the experimental setup were investigated in detail, such as the particle beam dynamics during the extraction process, the manufacturing and characterization of bent crystals, and the detection of the extracted beam. In order to optimize the crystal geometry, the overall process of beam extraction was simulated, taking into account the influence of radiation energy losses. As result it is concluded that the multi-turn electron beam extraction efficiency can reach up to 16%. In principle this crystal-based beam extraction technique can be applied at any electron synchrotron in order to provide multi-GeV electron beams in a parasitic mode. This technique will allow to supply fixed-target experiments by intense high-quality monoenergetic electron beams. Furthermore, electron/positron crystal-based extraction from future lepton colliders may provide an access to unique experimental conditions for ultra-high energy fixed-target experiments including searches for new physics beyond the Standard Model. [ABSTRACT FROM AUTHOR]

A graded Si1-xGex crystal has been manufactured for operation with high-energy protons to excite coherent interactions of the particles with the crystal such as channeling and volume reflection. The crystal had the shape of a parallelepiped though its (111) atomic planes were curved at a radius of 25.6 m because of the graded Ge content. The crystal was exposed to a 400 GeV/c proton beam at the external lines of CERN Super Proton Synchrotron to probe its capability to steer high-energy particles. Measured deflection efficiency was 62.0% under planar channeling and 96.0% under volume reflection. Such values are critically compared to their counterparts for a standard bent Si crystal under peer conditions. A Monte Carlo simulation of the dynamics of channeled and volume reflected particles in a graded crystal including the effect of Ge impurities and of lattice dislocations has been carried out. We found that the effect of crystal imperfections spoiled the efficiency of channeling while it negligibly affected the performance of volume reflection. We finally propose the usage of the graded crystal as a primary scatterer to aid halo collimation for the new generation of hadronic machines. As a unique feature, a properly cut graded crystal circumvents the problem of the miscut angle, which is currently a severe limitation for implementation of crystal-assisted collimation. [ABSTRACT FROM AUTHOR]

Lake Cadagno is a crenogenic meromictic lake situated in the southern range of the Swiss Alps characterized by a compact chemocline that has been the object of many ecological studies. The population dynamics of phototrophic sulfur bacteria in the chemocline has been monitored since 1994 with molecular methods such as 16S rRNA gene clone library analysis. To reconstruct paleo-microbial community dynamics, we developed a quantitative real-time PCR methodology for specific detection of 16S rRNA gene sequences of purple and green sulfur bacteria populations from sediment samples. We detected fossil 16S rDNA of nine populations of phototrophic sulfur bacteria down to 9-m sediment depth, corresponding to about 9500 years of the lake's biogeological history. These results provide the first evidence for the presence of 16S rDNA of anoxygenic phototrophic bacteria in Holocene sediments of an alpine meromictic lake and indicate that the water column stratification and the bacterial plume were already present in Lake Cadagno thousands of years ago. The finding of Chlorobium clathratiforme remains in all the samples analyzed shows that this population, identified in the water column only in 2001, was already a part of the lake's biota in the past. [ABSTRACT FROM AUTHOR]

Abstract: Permanent and reproducible deformation of silicon mono-crystals has been experimentally attained by mechanical grooving of one of its surfaces. The method produces uniform deformation that can be controlled by proper choice of the parameters of grooving. The strain in silicon plates was modeled analytically in terms of a superficial compression occurring in the material between the grooves. The superficial grooved region acts as if it were like a tensile film with the strain propagating deep into the bulk, which results in spherical and homogeneous curvature of the whole crystal plate. Thereby, the classic Stoney''s formula was reconsidered and adapted for explanation of the experimental behavior. Minimum radius of curvature experimentally achieved was about 3m. Curved crystals are the basis for many applications, e.g. for x-ray optics to manipulate high energy photons for the construction of very sensitive instruments for x-ray astronomy. [Copyright &y& Elsevier]

Abstract: In this work we report the synthesis, microstructure, electric and spectroscopic properties, and sensing performances of Ti x Sn1− x O2 (x =0.1, 0.2, 0.3, 0.5, 0.7, 0.9) nano-powders and of SnO2 and TiO2 reference samples, prepared via sol-gel route starting from metal-organic precursors working in hydro-alcoholic media. Actually, the attention is particularly focused on properties of the sample with x =0.2, in comparison with ones of the other solid solutions and of the single oxides. Indeed, this solid solution showed a borderline behaviour between that of the solid solution with x =0.1 and that of the other solid solutions with x ≥0.3. An abrupt change in the structural, electrical and spectroscopic properties has been observed, passing from sample with x =0.1, showing a behaviour very similar to that of SnO2, to one x =0.3 showing a behaviour very similar to that of TiO2. The borderline properties of the mixed oxide with x =0.2 represent the expected continuous transition among the two behaviours. [Copyright &y& Elsevier]

Abstract: One of the main applications of metal oxide gas sensors is the environmental monitoring of urban and industrial areas, where the pollution level may become dangerously high. In this frame, environmental temperature plays a fundamental role, since it may influence the sensor signal. This work aims at measuring ambient temperature induced conductance variation, and to suggest a theoretical model to account for that. [Copyright &y& Elsevier]

Abstract: Novel Ti x Sn1−x O2 (0.3< x <0.9) nanostructured oxides for gas sensing, have been synthesized and characterized through a great variety of investigation techniques, such as electron microscopy, X-ray diffraction, specific surface area measurements, UV–vis and IR spectroscopies, photoluminescence emission spectra and finally electrical measurements. All structural investigations showed solid solutions of the two single oxides; only the oxide with x =0.7 showed a beginning of spinodal decomposition revealed by XRD. Surprisingly, the samples with x =0.3 and 0.5 exhibited carbon monoxide response much higher than for pure SnO2. Investigations on this point, performed through spectroscopic measurements in the presence of CO, suggest a different behaviour of the solid solutions from the single oxides. [Copyright &y& Elsevier]

Abstract: Thin films of titania with the addition of niobium and tantalum have been achieved by reactive sputtering process. Structural and morphological studies have been carried out by means of XRD, RBS, TEM and AFM in order to correlate the microstructural features to the sensing performance of the layers. The films proved sensitive to ethanol and carbon monoxide and ammonia. In the case of niobium addition, it was shown that annealing temperature and niobium content strongly influence the gas response of the films converting a n-type response, which is typical of pure TiO2 and of most of metal-oxide sensors, to a p-type response; this peculiarity is crucial for the discrimination of different gases. In the case of tantalum addition, the annealing treatment at 800°C led only to a phase transformation that reduced the sensing performance of the layer. High sensitivity to CO is achieved with anatase or mixed anatase and rutile phases, while the rutile phase only exhibit a low gas sensitivity. [Copyright &y& Elsevier]

Abstract: Particle channeling in a bent crystal lattice has led to an efficient instrument for beam steering at accelerators [Biryukov et al., Crystal Channeling and its Application at High Energy Accelerators, Springer, Berlin, 1997], demonstrated from MeV to TeV energies. In particular, crystal focusing of high-energy protons to micron size has been demonstrated at IHEP with the results well in match with Lindhard (critical angle) prediction. Channeling in crystal microstructures has been proposed as a unique source of a microbeam of high-energy particles [Bellucci et al., Phys. Rev. ST Accel. Beams 6 (2003) 033502]. Channeling in nanostructures (single-wall and multi-wall nanotubes) offers the opportunities to produce ion beams on nanoscale. Particles channeled in a nanotube (with typical diameter of about 1nm) are trapped in two dimensions and can be steered (deflected, focused) with the efficiency similar to that of crystal channeling or better. This technique has been a subject of computer simulations, with experimental efforts under way in several high-energy labs, including IHEP. We present the theoretical outlook for making channeling-based nanoscale ion beams and report the experience with crystal-focused microscale proton beams. [Copyright &y& Elsevier]

We used SnO2 gas sensors for monitoring ethylene in the range of interest for fruit ripening. The effect of atmospheric humidity on the sensor conductance and response towards ethylene was quantitatively measured. An algorithm for humidity compensation of the sensor’s response was developed and applied to experimental data. The results of our analysis proved useful for the application of chemoresistive sensors for agro-alimentary monitoring. [Copyright &y& Elsevier]

The possibility to increase the surface-to-volume ratio of tin di-oxide thin films deposited through the RGTO technique is investigated. A novel strategy was used to increase the surface roughness and to exploit the catalytic and sensing properties of a W–Mo layer. Deposition consists in four steps: deposition by sputtering of W–Mo layer, first annealing process, deposition of metallic Sn, second annealing process. Electrical characterization shows a considerable increase in the conductivity of the combined layers and also an increase in the interactivity of the double layer compared to either pure SnO2 or W–Mo oxide layers. This can be ascribed both to the increase in the surface to volume ratio and to the catalytic effect of W and Mo oxide. [Copyright &y& Elsevier]

The design and manufacturing details of a new crystal deflector for proton beams are reported. The technique allows one to manufacture a very short deflector along the beam direction (2 mm). Thanks to that, multiple encounters of circulating particles with the crystal are possible with a reduced probability of multiple scattering and nuclear interactions per encounter. Thus, drastic increase in efficiency for particle extraction out of the accelerator was attained (85%) on a 70 GeV proton beam. We show the characteristics of the crystal deflector and the technology behind it. [ABSTRACT FROM AUTHOR]

We present some recent trends about research on gas sensors based on semiconducting thin films based on Ti, W, and Mo mixed oxides. The structural, electrical and gas-sensing properties of these films, deposited by rf reactive sputtering from composite targets of W–Mo, Ti–W and Ti–Mo at different abundance, were investigated through electron microscopy and volt-amperometric techniques. All of these layers showed sensing capability toward CO, NO2 or ethanol. The thin films obtained were able to detect CO, NO2, and ethanol below the concentration limit for environmental-monitoring and breath-analysis application. [Copyright &y& Elsevier]

Discusses the results of experiments conducted on a radio-frequency-based streak Camera. Magnetic deflection of the electron beam imparted by a radio-frequency cavity; Principles behind a radio frequency camera; Space-charge influence.

This work presents the design and validation of a measuring instrumentation for an easy, complete, and tunable characterization of chemiresistive gas sensors based on metal-oxide semiconductors. The equipment, described in depth both as hardware and as software, was designed to monitor the electrical behavior of gas sensors in controlled thermodynamic conditions. The main goal of this setup is to synchronize the electrical characterization with different measuring conditions, i.e., operating temperature, relative humidity, and gas target concentration. This operation allows us to automate various measurement protocols, otherwise impossible to obtain manually. In particular, this instrumentation permits to correlate the response of a chemiresistive gas sensor to the applied voltage, to its working temperature, and to the gas concentration, automating the acquisition of the current–voltage characteristic and the current–temperature characteristic (Arrhenius plot) of sensing films. The experimental setup was validated by reporting the electrical characterization of a standard metal-oxide-based gas sensing material, such as SnO2, working under different thermodynamic conditions. [ABSTRACT FROM AUTHOR]

The research investigates coherent interactions between sub-GeV electrons and oriented scintillator crystals, leading to enhanced electromagnetic (EM) radiation. Experiments at Mainz Mikrotron (MAMI) involved PWO, BGO, and CsI crystals oriented along 〈 100 〉 , 〈 111 〉 , and 〈 100 〉 axes, respectively. Enhanced radiation emission was observed when the beam was aligned with crystal axes, especially in BGO and CsI for the first time. These findings are crucial for innovative detectors using oriented crystal scintillators, amplifying EM processes along specific crystallographic directions. Potential applications include ultra-compact, highly sensitive electromagnetic calorimeters for high-energy physics and astroparticles, as well as high-performance gamma detectors for nuclear physics and medical imaging. [ABSTRACT FROM AUTHOR]

We used a GaAs crystal operating in a negative electron affinity mode to produce an intense continuous electron beam by photoemission. The major drawback of photoemission from GaAs, i.e., rapid current decay, was overcome without continuously supplying cesium. After a little initial decay, the current remained constant at 1 mA over a few mm2, with no degradation. Seasoning of the vacuum chamber played a fundamental role in achieving this performance. [ABSTRACT FROM AUTHOR]