Reduction of the radar cross section of arbitrarily shaped cavity structures

The problem of the reduction of the radar cross section (RCS) of open-ended cavities was studied. The issues investigated were reduction through lossy coating materials on the inner cavity wall and reduction through shaping of the cavity. A method was presented to calculate the RCS of any arbitrarily shaped structure in order to study the shaping problem. The limitations of this method were also addressed. The modal attenuation was studied in a multilayered coated waveguide. It was shown that by employing two layers of coating, it was possible to achieve an increase in both the magnitude of attenuation and the frequency band of effectiveness. The numerical method used in finding the roots of the characteristic equation breaks down when the coating thickness is very lossy and large in terms of wavelength. A new method of computing the RCS of an arbitrary cavity was applied to study the effects of longitudinal bending on RCS reduction. The ray and modal descriptions for the fields in a parallel plate waveguide were compared. To extend the range of validity of the Shooting and Bouncing Ray (SBR) method, the simple ray picture must be modified to account for the beam blurring

The role of right and left parietal lobes in the conceptual processing of numbers

Neuropsychological and functional imaging studies have associated the conceptual processing of numbers with bilateral parietal regions (including intraparietal sulcus). However, the processes driving these effects remain unclear because both left and right posterior parietal regions are activated by many other conceptual, perceptual, attention, and response-selection processes. To dissociate parietal activation that is number-selective from parietal activation related to other stimulus or response-selection processes, we used fMRI to compare numbers and object names during exactly the same conceptual and perceptual tasks while factoring out activations correlating with response times. We found that right parietal activation was higher for conceptual decisions on numbers relative to the same tasks on object names, even when response time effects were fully factored out. In contrast, left parietal activation for numbers was equally involved in conceptual processing of object names. We suggest that left parietal activation for numbers reflects a range of processes, including the retrieval of learnt facts that are also involved in conceptual decisions on object names. In contrast, number selectivity in right parietal cortex reflects processes that are more involved in conceptual decisions on numbers than object names. Our results generate a new set of hypotheses that have implications for the design of future behavioral and functional imaging studies of patients with left and right parietal damage

Comment on "Two Phase Transitions in the Fully frustrated XY Model"

The conclusions of a recent paper by Olsson (Phys. Rev. Lett. 75, 2758 (1995), cond-mat/9506082) about the fully frustrated XY model in two dimensions are questioned. In particular, the evidence presented for having two separate chiral and U(1) phase transitions are critically considered.Comment: One page one table, to Appear in Physical Review Letter

(2 Z )-3-Hydroxy-1-(pyridin-2-yl)-3-(pyridin-3-yl)prop-2-en-1one: crystal structure and Hirshfeld surface analysis

The title compound, C13H10N2O2 [also called 1-(pyridin-2-yl)-3-(pyridin-3-yl)propane-1,3-dione], features an almost planar (r.m.s. deviation = 0.0095 Å) central C3O2 core consolidated by an intra­molecular hy­droxy-O-H...O(carbon­yl) hydrogen bond. Twists are evident in the mol­ecule, as seen in the dihedral angles between the central core and the 2- and pyridin-3-yl rings of 8.91 (7) and 15.88 (6)°, respectively. The conformation about the C=C bond [1.3931 (17) Å] is Z, and the N atoms lie to the same side of the mol­ecule. In the mol­ecular packing, supra­molecular chains along the a axis are mediated by [pi](pyridin-2-yl)-[pi](pyridin-3-yl) inter­actions [inter-centroid distance = 3.7662 (9) Å]. The observation that chains pack with no directional inter­actions between them is consistent with the calculated electrostatic potential, which indicates that repulsive inter­actions dominate

Highly Coordinated Gene Regulation in Mouse Skeletal Muscle Regeneration

Mammalian skeletal muscles are capable of regeneration after injury. Quiescent satellite cells are activated to reenter the cell cycle and to differentiate for repair, recapitulating features of myogenesis during embryonic development. To understand better the molecular mechanism involved in this process in vivo, we employed high density cDNA microarrays for gene expression profiling in mouse tibialis anterior muscles after a cardiotoxin injection. Among 16,267 gene elements surveyed, 3,532 elements showed at least a 2.5-fold change at one or more time points during a 14-day time course. Hierarchical cluster analysis and semiquantitative reverse transcription-PCR showed induction of genes important for cell cycle control and DNA replication during the early phase of muscle regeneration. Subsequently, genes for myogenic regulatory factors, a group of imprinted genes and genes with functions to inhibit cell cycle progression and promote myogenic differentiation, were induced when myogenic stem cells started to differentiate. Induction of a majority of these genes, including E2f1 and E2f2, was abolished in muscles lacking satellite cell activity after gamma radiation. Regeneration was severely compromised in E2f1 null mice but not affected in E2f2 null mice. This study identifies novel genes potentially important for muscle regeneration and reveals highly coordinated myogenic cell proliferation and differentiation programs in adult skeletal muscle regeneration in vivo

Non-destructive quantitation of spermine in human prostate tissue samples using HRMAS 1H NMR spectroscopy at 9.4 T

AbstractWe present the results of a study of human prostate specimens evaluated by high resolution magic angle spinning 1H nuclear magnetic resonance (NMR) spectroscopy at 400 MHz (9.4 T) and by quantitative histopathology. We demonstrate that NMR and pathology data can be obtained from the same intact specimens, and report for the first time a linear correlation between the NMR measured concentration of spermine, a proposed endogenous inhibitor to prostate cancer growth, and the volume percentage of normal prostatic epithelial cells as quantified by histopathology. Our results show that NMR may serve as a critical tool for the investigation of the inhibitory mechanism of spermine in human subjects

Observational Constraints on Exponential Gravity

We study the observational constraints on the exponential gravity model of f(R)=-beta*Rs(1-e^(-R/Rs)). We use the latest observational data including Supernova Cosmology Project (SCP) Union2 compilation, Two-Degree Field Galaxy Redshift Survey (2dFGRS), Sloan Digital Sky Survey Data Release 7 (SDSS DR7) and Seven-Year Wilkinson Microwave Anisotropy Probe (WMAP7) in our analysis. From these observations, we obtain a lower bound on the model parameter beta at 1.27 (95% CL) but no appreciable upper bound. The constraint on the present matter density parameter is 0.245< Omega_m^0<0.311 (95% CL). We also find out the best-fit value of model parameters on several cases.Comment: 14pages, 3 figures, accepted by PR

Variations of the ISM Compactness Across the Main Sequence of Star-Forming Galaxies: Observations and Simulations

(abridged) The majority of star-forming galaxies follow a simple empirical correlation in the star formation rate (SFR) versus stellar mass ($M_*$) plane, usually referred to as the star formation Main Sequence (MS). Here we combine a set of hydro-dynamical simulations of interacting galactic disks with state-of-the-art radiative transfer codes to analyze how the evolution of mergers is reflected upon the properties of the MS. We present \textsc{Chiburst}, a Markov Chain Monte Carlo (MCMC) Spectral Energy Distribution (SED) code that fits the multi-wavelength, broad-band photometry of galaxies and derives stellar masses, star formation rates, and geometrical properties of the dust distribution. We apply this tool to the SEDs of simulated mergers and compare the derived results with the reference output from the simulations. Our results indicate that changes in the SEDs of mergers as they approach coalescence and depart from the MS are related to an evolution of dust geometry in scales larger than a few hundred parsecs. This is reflected in a correlation between the specific star formation rate (sSFR), and the compactness parameter $\mathcal{C}$, that parametrizes this geometry and hence the evolution of dust temperature ($T_{\rm{dust}}$) with time. As mergers approach coalescence, they depart from the MS and increase their compactness, which implies that moderate outliers of the MS are consistent with late-type mergers. By further applying our method to real observations of Luminous Infrared Galaxies (LIRGs), we show that the merger scenario is unable to explain these extreme outliers of the MS. Only by significantly increasing the gas fraction in the simulations are we able to reproduce the SEDs of LIRGs.Comment: 18 pages, 10 figures, accepted in Ap