Mechanisms of geometrical seismic attenuation

In several recent reports, we have explained the frequency dependence of the apparent seismic quality-factor (Q) observed in many studies according to the effects of geometrical attenuation, which was defined as the zerofrequency limit of the temporal attenuation coefficient. In particular, geometrical attenuation was found to be positive for most waves traveling within the lithosphere. Here, we present three theoretical models that illustrate the origin of this geometrical attenuation, and we investigate the causes of its preferential positive values. In addition, we discuss the physical basis and limitations of both the conventional and new attenuation models. For waves in media with slowly varying properties, geometrical attenuation is caused by variations in the wavefront curvature, which can be both positive (for defocusing) and negative (for focusing). In media with velocity/density contrasts, incoherent reflectivity leads to geometrical-attenuation coefficients which are proportional to the mean squared reflectivity and are always positive. For «coherent» reflectivity, the geometrical attenuation is approximately zero, and the attenuation process can be described according to the concept of «scattering Q». However, the true meaning of this parameter is in describing the mean reflectivity within the medium, and not that of the traditional resonator quality factor known in mechanics. The general conclusion from these models is that non-zero and often positive levels of geometrical attenuation are common in realistic, heterogeneous media, both observationally and theoretically. When transformed into the conventional Q-factor form, this positive geometrical attenuation leads to Q values that quickly increase with frequency. These predictions show that the positive frequency-dependent Q observed in many datasets might represent artifacts of the transformations of the attenuation coefficients into Q

A glycoprotein subunit vaccine elicits a strong Rift Valley fever virus neutralizing antibody response in sheep

Rift Valley fever virus (RVFV), a member of the Bunyaviridae family, is a mosquito-borne zoonotic pathogen that causes serious morbidity and mortality in livestock and humans. The recent spread of the virus beyond its traditional endemic boundaries in Africa to the Arabian Peninsula coupled with the presence of susceptible vectors in non-endemic countries has created increased interest in RVF vaccines. Subunit vaccines composed of specific virus proteins expressed in eukaryotic or prokaryotic expression systems are shown to elicit neutralizing antibodies in susceptible hosts. RVFV structural proteins, N-terminus glycoprotein (Gn) and C-terminus glycoprotein (Gc), were expressed using a recombinant baculovirus expression system. The recombinant proteins were reconstituted as GnGc subunit vaccine formulation and evaluated for immunogenicity in a target species, sheep. Six sheep were each immunized with a primary dose of 50 μg of each vaccine immunogen adjuvanted with montanide ISA25, and at day 21 post-vaccination, each animal received a second dose of the same vaccine. The vaccine induced strong antibody response in all animals as determined by indirect enzyme-linked immunosorbent assay (ELISA). Plaque reduction neutralization test (PRNT80) showed the primary dose of the vaccine was sufficient to elicit potentially protective virus neutralizing antibody titers ranging from 40 to 160, and the second vaccine dose boosted the titer to more than 1,280. Further, all animals tested positive for neutralizing antibodies at day 328 pv. ELISA analysis using the recombinant nucleocapsid protein as a negative marker antigen indicated that the vaccine candidate is DIVA (differentiating infected from vaccinated animals) compatible, and represents a promising vaccine platform for RVFV infection in susceptible species

RrmA regulates the stability of specific transcripts in response to both nitrogen source and oxidative stress

Differential regulation of transcript stability is an effective means by which an organism can modulate gene expression. A well-characterized example is glutamine signalled degradation of specific transcripts in Aspergillus nidulans. In the case of areA, which encodes a wide-domain transcription factor mediating nitrogen metabolite repression, the signal is mediated through a highly conserved region of the 3′ UTR. Utilizing this RNA sequence we isolated RrmA, an RNA recognition motif protein. Disruption of the respective gene led to loss of both glutamine signalled transcript degradation as well as nitrate signalled stabilization of niaD mRNA. However, nitrogen starvation was shown to act independently of RrmA in stabilizing certain transcripts. RrmA was also implicated in the regulation of arginine catabolism gene expression and the oxidative stress responses at the level of mRNA stability. ΔrrmA mutants are hypersensitive to oxidative stress. This phenotype correlates with destabilization of eifE and dhsA mRNA. eifE encodes eIF5A, a translation factor within which a conserved lysine is post-translationally modified to hypusine, a process requiring DhsA. Intriguingly, for specific transcripts RrmA mediates both stabilization and destabilization and the specificity of the signals transduced is transcript dependent, suggesting it acts in consort with other factors which differ between transcripts

Uniform Patterns of Fe Vacancy Ordering in the Kx(Fe,Co)2-ySe2 Superconductors

The Fe-vacancy ordering patterns in the superconducting KxFe2-ySe2 and non-superconducting Kx(Fe,Co)2-ySe2 samples have been investigated by electron diffraction and high angle annular dark field scanning transmission electron microscopy. The Fe-vacancy ordering occurs in the ab plane of the parent ThCr2Si2-type structure, demonstrating two types of patterns. The superstructure I retains the tetragonal symmetry and can be described with the aI = bI = as{\surd}5 (as is the unit cell parameter of the parent ThCr2Si2-type structure) supercell and I4/m space group. The superstructure II reduces the symmetry to orthorhombic with the aII = as{\surd}2, bII = 2as{\surd}2 supercell and the Ibam space group. This type of superstructure is observed for the first time in KxFe2-ySe2. The Fe-vacancy ordering is inhomogeneous: the disordered areas interleave with the superstructures I and II in the same crystallite. The observed superstructures represent the compositionally-dependent uniform ordering patterns of two species (the Fe atoms and vacancies) on a square lattice. More complex uniform ordered configurations, including compositional stripes, can be predicted for different chemical compositions of the KxFe2-ySe2 (0 < y < 0.5) solid solutions.Comment: This document is the unedited author's version of a Submitted Work that was subsequently accepted for publication in Chemistry of Materials (copyright American Chemical Society) after peer review. To access the final edited and published work see Chem. Mater. 2011, 23, 4311-4316. 17 pages, 8 figure

Screening vs. Confinement in 1+1 Dimensions

We show that, in 1+1 dimensional gauge theories, a heavy probe charge is screened by dynamical massless fermions both in the case when the source and the dynamical fermions belong to the same representation of the gauge group and, unexpectedly, in the case when the representation of the probe charge is smaller than the representation of the massless fermions. Thus, a fractionally charged heavy probe is screened by dynamical fermions of integer charge in the massless Schwinger model, and a colored probe in the fundamental representation is screened in $QCD_2$ with adjoint massless Majorana fermions. The screening disappears and confinement is restored as soon as the dynamical fermions are given a non-zero mass. For small masses, the string tension is given by the product of the light fermion mass and the fermion condensate with a known numerical coefficient. Parallels with 3+1 dimensional $QCD$ and supersymmetric gauge theories are discussed.Comment: 29 pages, latex, no figures. slight change in the wording on page 2, references adde

Mechanisms of geometrical seismic attenuation

Abstract In several recent papers, we explained the frequency dependence of the apparent seismic quality-factor (Q) observed in many studies by the effects of geometrical attenuation (GA), which was defined as the zero-frequency limit of the temporal attenuation coefficient. In particular, GA was found to be positive for most waves traveling within the lithosphere. Here, we present three theoretical models illustrating the origin of such GA, and investigate the causes of its preferential positive values. In addition, we discuss the physical basis and limitations of both the conventional and new attenuation models. For waves in media with slowly varying properties, GA is caused by variations of wavefront curvatures, which can be both positive (for defocusing) and negative (for focusing). In media with velocity/density contrasts, incoherent reflectivity leads to GA coefficients which are proportional to the mean squared reflectivity and always positive. For &quot;coherent&quot; reflectivity, the GA is approximately zero, and the attenuation process can be described by the concept of &quot;scattering Q.&quot; However, the true meaning of this parameter is in describing the mean reflectivity within the medium and not that of the traditional resonator quality factor known in mechanics. The general conclusion from these models is that non-zero and often positive levels of GA are common in realistic, heterogeneous media both observationally and theoretically. When transformed into the conventional Q-factor form, such positive GA leads to Q values quickly increasing with frequency. These predictions show that the positive frequency dependent Q observed in many datasets may represent artifacts of the 3 transformations of the attenuation coefficients into Q

Mechanisms of geometrical seismic attenuation

Abstract In several recent papers, we explained the frequency dependence of the apparent seismic quality-factor (Q) observed in many studies by the effects of geometrical attenuation (GA), which was defined as the zero-frequency limit of the temporal attenuation coefficient. In particular, GA was found to be positive for most waves traveling within the lithosphere. Here, we present three theoretical models illustrating the origin of such GA, and investigate the causes of its preferential positive values. In addition, we discuss the physical basis and limitations of both the conventional and new attenuation models. For waves in media with slowly varying properties, GA is caused by variations of wavefront curvatures, which can be both positive (for defocusing) and negative (for focusing). In media with velocity/density contrasts, incoherent reflectivity leads to GA coefficients which are proportional to the mean squared reflectivity and always positive. For &quot;coherent&quot; reflectivity, the GA is approximately zero, and the attenuation process can be described by the concept of &quot;scattering Q.&quot; However, the true meaning of this parameter is in describing the mean reflectivity within the medium and not that of the traditional resonator quality factor known in mechanics. The general conclusion from these models is that non-zero and often positive levels of GA are common in realistic, heterogeneous media both observationally and theoretically. When transformed into the conventional Q-factor form, such positive GA leads to Q values quickly increasing with frequency. These predictions show that the positive frequency dependent Q observed in many datasets may represent artifacts of the transformations of the attenuation coefficients into Q