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Ultraperipheral collisions in hadron colliders give new opportunities to investigate the hadron structure through exclusive photoproduction processes. We describe the possibility of measuring the Generalized Parton Distributions in the Timelike Compton Scattering process and in the production of heavy vector meson.
Ultra-peripheral collisions (UPCs) of heavy ions involve long range electromagnetic interactions at impact parameters larger than twice the nuclear radius. At TeV energies, the strong electromagnetic field due to the coherent action of the Z = 82 proton charges generates a large flux of photons, which can be used for high-energy photoproduction studies. Heavy vector mesons produced in electromagnetic interactions provide direct information on the parton distribution functions in the nucleus at very low values of Bjorken-x. These events are characterized by a very low hadron multiplicity. The wide pseudo-rapidity coverage of the CMS detectors is used to separate such events from very peripheral nuclear interactions. The CMS experiment has excellent capabilities for the measurement of the heavy vector mesons in the dimuon decay channel using the tracker and the muon chambers. This analysis demonstrates CMS’s capabilities for measuring J/ψ and the two-photon process in ultra-peripheral collisions, using the 2011 PbPb and 2013 pPb data. The prospects for future measurements using the data to be collected in the 2015 PbPb run will be described.
The new results on measurement of dijet production in diffractive deep inelastic ep scattering, ep → eXY, obtained with the H1 detector are presented. The system X contains at least two jets. Measurements are performed using two approaches. One approach is based on detection of the diffractive processes with Y being a proton or its low mass excitation. Diffractive events are selected by demanding a large empty rapidity gap interval separating the final state hadronic systems X and Y. In another approach, the leading final state proton from the process ep → eXp is detected in the H1 Very Forward Proton Spectrometer. The measurements are compared with predictions from NLO QCD calculations based on diffractive parton densities.
The objective of this paper is to improve the power conversion efficiency of HIT solar cell using amorphous materials. A high efficiency amorphous material based on two dimensional heterojunction solar cell with thin intrinsic layer is designed and simulated at the research level using Synopsys/RSOFT-Solar Cell utility. The HIT structure composed of TCO/a-Si:H(p)/a-Si:H(i)/c-Si(n)/a-Si:H(i)/a-Si:H(n{sup +})/Ag is created by using of RSOFT CAD. Optical characterization of the cell is performed by Diffract MOD model based on RCWA (rigorous coupled wave analysis) algorithm. Electrical characterization of the cell is done by Solar cell utility using based on Ideal diode method. In addition, optimization of the different layer thickness in the HIT structure is executed to improve the absorption and thereby the photocurrent density. The proposed HIT solar cell structure resulted in an open circuit voltage of 0.751 V, a short circuit current density of 36.37 mA/cm{sup 2} and fill factor of 85.37% contributing to the total power conversion efficiency of 25.91% under AM1.5G. Simulation results showed that the power conversion efficiency is improved by 1.21% as compared to the reference HIT solar cell. This improvement in high efficiency is due to reduction of resistive losses, recombination losses at the hetero junction interface between intrinsic a-Si and c-Si, and optimization of the thicknesses in a-Si and c-Si layers.
To enhance the solubility of orally administered pharmaceuticals, liquid capsules or amorphous tablets are often preferred over crystalline drug products. However, little is known regarding the variation in bonding mechanisms between pharmaceutical molecules in their different disordered forms. In this study, liquid and melt-quenched glassy carbamazepine have been studied using high energy X-ray diffraction and modeled using Empirical Potential Structure Refinement. The results show significant structural differences between the liquid and glassy states. The liquid shows a wide range of structures; from isolated molecules, to aromatic ring correlations and NH-O hydrogen bonding. Upon quenching from the liquid to the glass the number of hydrogen bonds per molecule increases by ~50% at the expense of a ~30% decrease in the close contact (non-bonded) carbon-carbon interactions between aromatic rings. During the cooling process, there is an increase in both singly and doubly hydrogen-bonded adjacent molecules. Although hydrogen-bonded dimers found in the crystalline states persist in the glassy state, the absence of a crystalline lattice also allows small, hydrogen-bonded NH-O trimers and tetramers to form. This proposed model for the structure of glassy carbamazepine is consistent with the results from vibrational spectroscopy and nuclear magnetic resonance.
ACS antenna patterns were computed using the Geometrical Theory of Diffraction (GTD) modeling technique in which the multipath interference from the Space Station structures was included. The accuracy of the numerical results obtained is verified by comparing them against a series of RF anechoic chamber measurements. Less than 1 dB degradation is expected if a +/- 15 deg cone is used to protect the ACS high gain antenna boresight pattern; a +/- 20 deg cone is required if no more than 0.5 dB gain degradation is desired.
The proposed work addresses two main objectives: (1) to pursue the development of the random diffraction screen model for analytical/computational characterization of the extinction and near-forward scattering by ring models that include particle crowding, uniform clustering, and clustering along preferred orientations (anisotropy). The characterization is crucial for proper interpretation of past (Voyager) and future (Cassini) ring, occultation observations in terms of physical ring properties, and is needed to address outstanding puzzles in the interpretation of the Voyager radio occultation data sets; (2) to continue the development of spectral analysis techniques to identify and characterize the power scattered by all features of Saturn's rings that can be resolved in the Voyager radio occultation observations, and to use the results to constrain the maximum particle size and its abundance. Characterization of the variability of surface mass density among the main ring, features and within individual features is important for constraining the ring mass and is relevant to investigations of ring dynamics and origin. We completed the developed of the stochastic geometry (random screen) model for the interaction of electromagnetic waves with of planetary ring models; used the model to relate the oblique optical depth and the angular spectrum of the near forward scattered signal to statistical averages of the stochastic geometry of the randomly blocked area. WE developed analytical results based on the assumption of Poisson statistics for particle positions, and investigated the dependence of the oblique optical depth and angular spectrum on the fractional area blocked, vertical ring profile, and incidence angle when the volume fraction is small. Demonstrated agreement with the classical radiative transfer predictions for oblique incidence. Also developed simulation procedures to generate statistical realizations of random screens corresponding to uniformly packed ring models, and used the results to characterize dependence of the extinction and near-forward scattering on ring thickness, packing fraction, and the ring opening angle.
Spectroscopic analyses have shown that smectites enhanced in the laboratory with additional ferric species exhibit important similarities to those of the soils on Mars. Ferrihydrite in these chemically treated smectites has features in the visible to near-infrared region that resemble the energies and band strengths of features in reflectance spectra observed for several bright regions on Mars. New samples have been prepared with sulfate as well, because S was found by Viking to be a major component in the surface material on Mars. A suite of ferrihydrite-bearing and ferric sulfate-bearing montmorillonites, prepared with variable Fe3+ and S concentrations and variable pH conditions, has been analyzed using reflectance spectroscopy in the visible and infrared regions, Mossbauer spectroscopy at room temperature and 4 K, differential thermal analysis, and X-ray diffraction. These analyses support the formation of ferrihydrite of variable crystallinity in the ferrihydrite-bearing montmorillonites and a combination of schwertmannite and ferrihydrite in the ferric sulfate-bearing montmorillonites. Small quantities of poorly crystalline or nanophase forms of other ferric materials may also be present in these samples. The chemical formation conditions of the ferrihydrite-bearing and ferric sulfate-bearing montmorillonites influence the character of the low temperature Mossbauer sextets and the visible reflectance spectra. An absorption minimum is observed at 0.88-0.89 micrometers in spectra of the ferric sulfate-bearing samples, and at 0.89-0.92 micrometers in spectra of the ferrihydrate-bearing montmorillonites. Mossbauer spectra of the ferric sulfate-bearing montmorillonites indicate variable concentrations of ferrihydrite and schwertmannite in the interlaminar spaces and along grain surfaces. Dehydration under reduced atmospheric pressure conditions induces a greater effect on the adsorbed and interlayer water in ferrihydrite-bearing montmorillonite than on the water in ferric sulfate-bearing montmorillonite. Reflectance spectra of ferric sulfate-bearing montmorillonite include a strong 3-micrometers band that is more resistant to dry atmospheric conditions than the 3-micrometers band in spectra of similarly prepared ferrihydrite-bearing montmorillonites.
Performance of X-ray reflectors affects that of X-ray mirrors. Modern X-ray mirrors have thousands of reflectors to gain large effective area. Evaluation of the reflectors is an important process in production of the mirrors. A diffraction pattern dominates reflector image when the parallel optical beam illuminates the reflector along its optical axis because the reflectors are used at grazing incident angles of around 1 deg and their effective width are 1–10 mm. A diffraction pattern from the entire reflector surface can be acquired at once with the aid of a lens. The diffraction pattern holds information of the surface profiles of the reflectors. To quantitatively evaluate the reflectors with the diffraction pattern, we created a diffraction pattern model by the wave optics with the ideal surface profile and fitted it to data. As a result, a correlation between fitting residual and the normal vector distribution of the surface profile was found. With our method, the reflectors can be evaluated and sorted out more efficiently.
This work reports on the computation of the average phase of a beam over an optical element via discrete Fourier transform techniques.
Optical diffraction and wavefront sensing and control (WFSC) models validated against the high-fidelity Roman Space Telescope Coronagraph Instrument (CGI) testbed play a key role in mask design selection and the verification of many requirements that cannot be accomplished until the observatory is in orbit. We have been steadily improving our model fidelity for the as-built CGI testbed system, demonstrating recently good agreement between measurements and model predictions while validating the Hybrid Lyot Coronagraph’s (HLC) performance using the in-orbit high order wavefront sensing and control (HOWFSC) operational scenario. We present modeling and testbed validation results that explain the reason many testbed WFSC iterations were needed for HLC in the past. A new, direct application of model-generated deformable mirror (DM) solutions has since been successfully demonstrated on the testbed with significant speed and performance improvement. The benefit of using such a solution opens up new model-based WFSC approaches for CGI. This can greatly reduce flight risk from potentially insufficient ground solution generation due to schedule or cost constraints or from unexpected post-delivery changes.
It is shown that the X-ray diffraction patterns from the Hendricks-Teller model for layered systems and the icosahedral glass models for the icosahedral phases show large fluctuations between nearby scattering wave vectors and from sample to sample, that are quite analogous to laser speckle. The statistics of these fluctuations are studied analytically for the first model and via computer simulations for the second. The observability of these effects is discussed briefly.
In this study, a model considering an asymmetric power heat distribution, temperature-dependent material properties, strain hardening and phase transformation was developed to predict temperature field and residual stress distribution in GTA dissimilar weld between austenitic stainless steel (304) and low carbon steel (1018). The effect of martensite formation on longitudinal and transverse residual stress distributions were investigated using both FE model and neutron diffraction measurement. The results indicate that martensitic phase has a significant influence on both residual stress components, i.e., transverse and longitudinal, and it not only can change the distribution shape of residual stress near the weld center line but, also, can alter the peak value of the residual stresses. The calculated temperature and weld zone profile were in agreement with the experimental results. Favorable general agreement was also found between the calculated residual stress distribution and residual stress measurements by the neutron diffraction method.
Presentation of the modeling and simulations for a pulsed x-ray source (LO-PXS) for dynamic diffraction studies.
An integrated in-situ neutron diffraction and elastic plastic self-consistent crystal plasticity (EPSC-CP) modeling scheme is performed on a binary Al–12Ce alloy and a ternary Al–12Ce–0.4Mg alloys. Using this scheme, the constitutive parameters, i.e. elastic constants and slip system parameters of individual phases can be calibrated which can be used in microstructure-based CP models to predict materials performance. From this study, it is shown that the elastic constants of Al 11 Ce 3 intermetallics calculated from density function theory calculation in the literature are rather accurate. When applied to the EPSC-CP model, the lattice strains of both the binary and ternary alloys are correctly predicted as compared with experiments, and large lattice strain differences between Al (100) plane and Al 11 Ce 3 (010) plane are demonstrated. The slip system parameters calibrated by the scheme shows that the addition of 0.4 wt% Mg in the alloy has little influence on the critical resolved shear stress of initial dislocation glide in the Al matrix which caused plastic yield in the material. This can be explained by the very dilute Mg solute content in the Al solid solution, causing large spacing of Al–Mg lattice misfit sites and little impact on resistance of dislocation glide at initial yield. The 0.4 wt% Mg addition, on the other hand, has a large influence on the hardening term in the slip system parameters, indicating those Al–Mg misfit sites do help dislocation accumulation during the deformation. The impact of dilute Mg addition on the Al slip system parameters is also reflected in the flow behavior of the ternary alloy: little impact on the yield stress, but a large impact on working hardening and tensile strength of the materials which is consistent with the literature.
X-ray Server (https://x-server.gmca.aps.anl.gov) is a collection of programs for online modelling of X-ray diffraction and scattering. Additionally, the dynamical diffraction program is the second most popular Server program, contributing 34% of total Server usage. It models dynamical X-ray diffraction from strained crystals and multilayers for any Bragg-case geometry including grazing incidence and exit. This paper reports on a revision of equations used by the program, which yields ten times faster calculations in most use cases, on implementing calculations of X-ray standing waves and on adding new options for modelling diffraction from monolayers.