Evaluation of point defect concentrations in B2-FeAl intermetallic compound

Thermal defects are studied for three compositions (49, 50 and 52 at.%Fe) of the intermetallic compound FeAl with B2 structure. Magnetic measurements are used to determine the thermal defect concentrations. These concentrations are determined from fitting the experimental curves of magnetic susceptibility, obtained during an isochronal annealing after a quench. Next we have evaluated theoretically the concentrations of different point defects that exist in this compound. The used model is based in the Bragg-Williams approximation assuming the nearest-neighbour interaction. The calculated concentrations describe well the experimental values.Thermal defects are studied for three compositions (49, 50 and 52 at.%Fe) of the intermetallic compound FeAl with B2 structure. Magnetic measurements are used to determine the thermal defect concentrations. These concentrations are determined from fitting the experimental curves of magnetic susceptibility, obtained during an isochronal annealing after a quench. Next we have evaluated theoretically the concentrations of different point defects that exist in this compound. The used model is based in the Bragg-Williams approximation assuming the nearest-neighbour interaction. The calculated concentrations describe well the experimental values

Non-linear macroscopic polarization in III-V nitride alloys

We study the dependence of macroscopic polarization on composition and strain in wurtzite III-V nitride ternary alloys using ab initio density-functional techniques. The spontaneous polarization is characterized by a large bowing, strongly dependent on the alloy microscopic structure. The bowing is due to the different response of the bulk binaries to hydrostatic pressure, and to internal strain effects (bond alternation). Disorder effects are instead minor. Deviations from parabolicity (simple bowing) are of order 10 % in the most extreme case of AlInN alloy, much less at all other compositions. Piezoelectric polarization is also strongly non-linear. At variance with the spontaneous component, this behavior is independent of microscopic alloy structure or disorder effects, and due entirely to the non-linear strain dependence of the bulk piezoelectric response. It is thus possible to predict the piezoelectric polarization for any alloy composition using the piezoelectricity of the parent binaries.Comment: RevTex 7 pages, 7 postscript figures embedde

Accurate calculation of polarization-related quantities in semiconductors

We demonstrate that polarization-related quantities in semiconductors can be predicted accurately from first-principles calculations using the appropriate approach to the problem, the Berry-phase polarization theory. For III-V nitrides, our test case, we find polarizations, polarization differences between nitride pairs, and piezoelectric constants quite close to their previously established values. Refined data are nevertheless provided for all the relevant quantities.Comment: RevTeX 4 pages, no figure

First-principles prediction of structure, energetics, formation enthalpy, elastic constants, polarization, and piezoelectric constants of AlN, GaN, and InN: comparison of local and gradient-corrected density-functional theory

A number of diverse bulk properties of the zincblende and wurtzite III-V nitrides AlN, GaN, and InN, are predicted from first principles within density functional theory using the plane-wave ultrasoft pseudopotential method, within both the LDA (local density) and GGA (generalized gradient) approximations to the exchange-correlation functional. Besides structure and cohesion, we study formation enthalpies (a key ingredient in predicting defect solubilities and surface stability), spontaneous polarizations and piezoelectric constants (central parameters for nanostructure modeling), and elastic constants. Our study bears out the relative merits of the two density functional approaches in describing diverse properties of the III-V nitrides (and of the parent species N$_2$, Al, Ga, and In), and leads us to conclude that the GGA approximation, associated with high-accuracy techniques such as multiprojector ultrasoft pseudopotentials or modern all-electron methods, is to be preferred in the study of III-V nitrides.Comment: RevTeX 6 pages, 12 tables, 0 figure

Testing the interaction of dark energy to dark matter through the analysis of virial relaxation of clusters Abell Clusters A586 and A1689 using realistic density profiles

Interaction between dark energy and dark matter is probed through deviation from the virial equilibrium for two relaxed clusters: A586 and A1689. The evaluation of the virial equilibrium is performed using realistic density profiles. The virial ratios found for the more realistic density profiles are consistent with the absence of interaction.Comment: 16pp 1 fig; accepted by GeR

Recent progress in the discovery of macrocyclic compounds as potential anti-infective therapeutics

Novel therapeutic strategies are urgently needed for the treatment of serious diseases caused by viral, bacterial and parasitic infections, because currently used drugs are facing the problem of rapidly emerging resistance. There is also an urgent need for agents that act on novel pathogen-specific targets, in order to expand the repertoire of possible therapies. The high throughput screening of diverse small molecule compound libraries has provided only a limited number of new lead series, and the number of compounds acting on novel targets is even smaller. Natural product screening has traditionally been very successful in the anti-infective area. Several successful drugs on the market as well as other compounds in clinical development are derived from natural products. Amongst these, many are macrocyclic compounds in the 1-2 kDa size range. This review will describe recent advances and novel drug discovery approaches in the anti-infective area, focusing on synthetic and natural macrocyclic compounds for which in vivo proof of concept has been established. The review will also highlight the Protein Epitope Mimetics (PEM) technology as a novel tool in the drug discovery process. Here the structures of naturally occurring antimicrobial and antiviral peptides and proteins are used as starting points to generate novel macrocyclic mimetics, which can be produced and optimized efficiently by combinatorial synthetic methods. Several recent examples highlight the great potential of the PEM approach in the discovery of new anti-infective agents

Development of HPD Clusters for MAGIC-II

MAGIC-II is the second imaging atmospheric Cherenkov telescope of the MAGIC observatory, which has recently been inaugurated on Canary island of La Palma. We are currently developing a new camera based on clusters of hybrid photon detectors (HPD) for the upgrade of MAGIC-II. The photon detectors feature a GaAsP photocathode and an avalanche diode as electron bombarded anodes with internal gain, and were supplied by Hamamatsu Photonics K.K. (R9792U-40). The HPD camera with high quantum efficiency will increase the MAGIC-II sensitivity and lower the energy threshold. The basic performance of the HPDs has been measured and a prototype of an HPD cluster has been developed to be mounted on MAGIC-II. Here we report on the status of the HPD cluster and the project of eventually using HPD clusters in the central area of the MAGIC-II camera.Comment: Contribution to the 31st ICRC, Lodz, Poland, July 200

Unveiling the population of orphan Gamma Ray Bursts

Gamma Ray Bursts are detectable in the gamma-ray band if their jets are oriented towards the observer. However, for each GRB with a typical theta_jet, there should be ~2/theta_jet^2 bursts whose emission cone is oriented elsewhere in space. These off-axis bursts can be eventually detected when, due to the deceleration of their relativistic jets, the beaming angle becomes comparable to the viewing angle. Orphan Afterglows (OA) should outnumber the current population of bursts detected in the gamma-ray band even if they have not been conclusively observed so far at any frequency. We compute the expected flux of the population of orphan afterglows in the mm, optical and X-ray bands through a population synthesis code of GRBs and the standard afterglow emission model. We estimate the detection rate of OA by on-going and forthcoming surveys. The average duration of OA as transients above a given limiting flux is derived and described with analytical expressions: in general OA should appear as daily transients in optical surveys and as monthly/yearly transients in the mm/radio band. We find that ~ 2 OA yr^-1 could already be detected by Gaia and up to 20 OA yr^-1 could be observed by the ZTF survey. A larger number of 50 OA yr^-1 should be detected by LSST in the optical band. For the X-ray band, ~ 26 OA yr^-1 could be detected by the eROSITA. For the large population of OA detectable by LSST, the X-ray and optical follow up of the light curve (for the brightest cases) and/or the extensive follow up of their emission in the mm and radio band could be the key to disentangle their GRB nature from other extragalactic transients of comparable flux density.Comment: 9 pages, 4 figures, 2 tables. Accepted for publication by Astronomy and Astrophysic

Use of Limpograss as an Alternative Feed During the Fall Forage Gap in Beef and Dairy Systems in Central and North Florida

In central and North Florida, the use of limpograss [Hemarthria altissima (Poir.) Stapf & C. E. Hubb.] for beef and dairy operations is limited and its potential use is not well documented. Two on-farm projects have been conducted in Central and North Florida to explore the use of limpograss as an alternative conserved forage during late fall and winter. The potential use of this forage as baleage for dairy farmers and as stockpiling for livestock producers would offer another alternative to reduce feed costs and fill the forage gap in the area when typical warm-season forages go dormant. In addition, the on-farm limpograss establishment would serve as dissemination for the limpograss planting material. Four dairy farms in Central and North Florida were enrolled in the study to evaluate two cultivars of limpograss for their potential when conserved as baleage. Four 0.2 ha strips were planted per farm, two for each variety (‘Kenhy’ and ‘Gibtuck’). The strips were arranged in a randomized complete block design, with two replicates in each location. Before wrapping the harvested forage for baleage, samples were taken to evaluate crude protein (CP) and in vitro digestible organic matter concentration (IVDOM). In addition, samples of fresh baleage at 60 and 90 d were analyzed for fermentation profile (pH, organic acids, and ammonia). Four beef cattle farms in North Florida allowed us to plant 1 ha of ‘Gibtuck’ for stockpiling evaluating the nutritive value at 30, 60, 90, and 120 days. Each plot was replicated four times and allocated in a randomized complete block design. The fermentation profile from the bales does not show differences between cultivars (P \u3e 0.05) and the pH is lower than 5 indicating that the fermentation process was successful. The CP and IVDOM of the stockpiling limpograss were different among the treatments (P \u3c 0.001)