Geostationary payload concepts for personal satellite communications

This paper reviews candidate satellite payload architectures for systems providing world-wide communication services to mobile users equipped with hand-held terminals based on large geostationary satellites. There are a number of problems related to the payload architecture, on-board routing and beamforming, and the design of the S-band Tx and L-band Rx antenna and front ends. A number of solutions are outlined, based on trade-offs with respect to the most significant performance parameters such as capacity, G/T, flexibility of routing traffic to beams and re-configuration of the spot-beam coverage, and payload mass and power. Candidate antenna and front-end configurations were studied, in particular direct radiating arrays, arrays magnified by a reflector and active focused reflectors with overlapping feed clusters for both transmit (multimax) and receive (beam synthesis). Regarding the on-board routing and beamforming sub-systems, analog techniques based on banks of SAW filters, FET or CMOS switches and cross-bar fixed and variable beamforming are compared with a hybrid analog/digital approach based on Chirp Fourier Transform (CFT) demultiplexer combined with digital beamforming or a fully digital processor implementation, also based on CFT demultiplexing

Black hole solutions in the warped DGP braneworld

We study the static, analytical solution of black holes in the warped DGP braneworld scenario. We show that the linearized field equations and matching conditions lead to solutions that are not compatible with Schwarzschild-(A)dS$_{(4)}$ solutions on the brane. This incompatibility is similar to vDVZ discontinuity in massive gravity theory. Following the standard procedure to remove this discontinuity, which firstly was proposed by Vainshtein, we keep some appropriate nonlinear terms in the field equations. This strategy has its origin in the fact that the spatial extrinsic curvature of the brane plays a crucial role in the nonlinear nature of the solutions and also in recovering the well-measured predictions of General Relativity (GR) at small scales. Using this feature, we obtained an interesting black string solution in the bulk when it is compatible with 4D GR solutions on the brane.Comment: 15 pages, no figure

Example of a self-consistent solution for a fermion on domain wall

We discuss a self-consistent solution for a fermion coupled to static scalar field in the form of a kink (domain wall). In particular, we study the case when the fermion occupies an excited non-zero frequency level in the presence of the domain wall field. The effect of the domain wall profile distortion is calculated analytically.Comment: 9 pages, no figures; minor corrections, one reference added, results unchange

Lipidomics Provides New Insight into Pathogenesis and Therapeutic Targets of the Ischemia-Reperfusion Injury

Lipids play an essential role in both tissue protection and damage. Tissue ischemia creates anaerobic conditions in which enzyme inactivation occurs, and reperfusion can initiate oxidative stress that leads to harmful changes in membrane lipids, the formation of aldehydes, and chain damage until cell death. The critical event in such a series of harmful events in the cell is the unwanted accumulation of fatty acids that leads to lipotoxicity. Lipid analysis provides additional insight into the pathogenesis of ischemia/reperfusion (I/R) disorders and reveals new targets for drug action. The profile of changes in the composition of fatty acids in the cell, as well as the time course of these changes, indicate both the mechanism of damage and new therapeutic possibilities. A therapeutic approach to reperfusion lipotoxicity involves attenuation of fatty acids overload, i.e., their transport to adipose tissue and/or inhibition of the adverse effects of fatty acids on cell damage and death. The latter option involves using PPAR agonists and drugs that modulate the transport of fatty acids via carnitine into the interior of the mitochondria or the redirection of long-chain fatty acids to peroxisomes

Homogeneity, Flatness and "Large" Extra Dimensions

We consider a model in which the universe is the direct product of a (3+1)-dimensional Friedmann, Robertson-Walker (FRW) space and a compact hyperbolic manifold (CHM). Standard Model fields are confined to a point in the CHM (i.e. to a brane). In such a space, the decay of massive Kaluza-Klein modes leads to the injection of any initial bulk entropy into the observable (FRW) universe. Both Kolmogoro-Sinai mixing due to the non-integrability of flows on CHMs and the large statistical averaging inherent in the collapse of the initial entropy onto the brane smooth out any initial inhomogeneities in the distribution of matter and of 3-curvature on any slice of constant 3-position. If, as we assume, the initial densities and curvatures in each fundamental correlation volume are drawn from some universal underlying distributions independent of location within the space, then these smoothing mechanisms effectively reduce the density and curvature inhomogeneities projected onto the FRW. This smoothing is sufficient to account for the current homogeneity and flatness of the universe. The fundamental scale of physics can be \gsim 1TeV. All relevant mass and length scales can have natural values in fundamental units. All large dimensionless numbers, such as the entropy of the universe, are understood as consequences of the topology of spacetime which is not explained. No model for the origin of structure is proffered.Comment: minor changes, matches version published in Phys. Rev. Let

Resistance to DNA Damaging agents produced invasive phenotype of rat glioma cells-characterization of a new in vivo model

Chemoresistance and invasion properties are severe limitations to efficient glioma therapy. Therefore, development of glioma in vivo models that more accurately resemble the situation observed in patients emerges. Previously, we established RC6 rat glioma cell line resistant to DNA damaging agents including antiglioma approved therapies such as 3-bis(2-chloroethyl)-1-nitrosourea (BCNU) and temozolomide (TMZ). Herein, we evaluated the invasiveness of RC6 cells in vitro and in a new orthotopic animal model. For comparison, we used C6 cells from which RC6 cells originated. Differences in cell growth properties were assessed by real-time cell analyzer. Cells’ invasive potential in vitro was studied in fluorescently labeled gelatin and by formation of multicellular spheroids in hydrogel. For animal studies, fluorescently labeled cells were inoculated into adult male Wistar rat brains. Consecutive coronal and sagittal brain sections were analyzed 10 and 25 days post-inoculation, while rats’ behavior was recorded during three days in the open field test starting from 25th day post-inoculation. We demonstrated that development of chemoresistance induced invasive phenotype of RC6 cells with significant behavioral impediments implying usefulness of orthotopic RC6 glioma allograft in preclinical studies for the examination of new approaches to counteract both chemoresistance and invasion of glioma cells

Stable branches of a solution for a fermion on domain wall

We discuss the case when a fermion occupies an excited non-zero frequency level in the field of domain wall. We demonstrate that a solution exists for the coupling constant in the limited interval $1<g<g_{max}\approx 1.65$. We show that indeed there are different branches of stable solution for $g$ in this interval. The first one corresponds to a fermion located on the domain wall ($1<g<\sqrt[4]{2\pi}$). The second branch, which belongs to the interval $\sqrt[4]{2\pi}\le g\le g_{max}$, describes a polarized fermion off the domain wall. The third branch with $1<g<g_{max}$ describes an excited antifermion in the field of the domain wall.Comment: 15 pages, 7 figures, references adde

Andreev Bound States and Self-Consistent Gap Functions for SNS and SNSNS Systems

Andreev bound states in clean, ballistic SNS and SNSNS junctions are calculated exactly and by using the Andreev approximation (AA). The AA appears to break down for junctions with transverse dimensions chosen such that the motion in the longitudinal direction is very slow. The doubly degenerate states typical for the traveling waves found in the AA are replaced by two standing waves in the exact treatment and the degeneracy is lifted. A multiple-scattering Green's function formalism is used, from which the states are found through the local density of states. The scattering by the interfaces in any layered system of ballistic normal metals and clean superconducting materials is taken into account exactly. The formalism allows, in addition, for a self-consistent determination of the gap function. In the numerical calculations the pairing coupling constant for aluminum is used. Various features of the proximity effect are shown

Neutrophil gelatinase associated lipocalin (NGAL) is elevated in type 2 diabetics with carotid artery stenosis and reduced under metformin treatment

Abstract Background Neutrophil gelatinase-associated lipocalin (NGAL), an acute phase protein released by neutrophils, has been described as biomarker of inflammatory states. Type 2 diabetes mellitus (T2DM) is characterized by increased inflammation and an elevated risk for embolization of carotid artery stenosis (CAS). We aimed to explore the role of NGAL systemically and in plaques of diabetics undergoing carotid endarterectomy. Moreover, the potential anti-inflammatory effect of metformin on NGAL was addressed in diabetics. Methods Serum NGAL and matrix metalloproteinase (MMP)-9/NGAL levels were measured in 136 patients (67 with T2DM vs. 69 non-diabetics) by specific ELISA. Endarterectomy samples were graded histologically according to the American Heart Association´s classification. NGAL mRNA expression was detected using RealTime-PCR in carotid endarterectomy specimens. Results Serum NGAL [median 107.4 ng/ml (quartiles: 75.2–145.0) vs. 64.4 (50.4 –81.3), p < 0.0001] and MMP-9/NGAL [41.5 ng/ml (20.8–63.9) vs. 27.6 (16.0–42.4), p = 0.017] were significantly elevated in diabetics compared to non-diabetics, as were leukocytes, neutrophils, C-reactive protein and fibrinogen (all p < 0.05). In patients with symptomatic and asymptomatic CAS diabetics had higher NGAL levels compared to non-diabetics [128.8 ng/ml (100.8–195.6) vs. 64.8 (48.9–82.2] and [101.6 ng/ml (70.1–125.3) vs. 63.8 (51.0–81.3), respectively, both p < 0.0001]. Presence of T2DM and type VI plaques (with surface defect, hemorrhage or thrombus) had a profound impact on NGAL levels (both p < 0.01) in multiple linear regression analysis. NGAL mRNA was detectable in 95% of analyzed carotid artery lesions of diabetics compared to 5% of non-diabetics (p < 0.0001). Accordingly, cerebral embolization was more frequent in diabetics (52.2% vs. 29%, p = 0.006). Metformin treatment was associated with decreased NGAL [60.7 ng/ml (51.9–69.2) vs. 121.7 (103.7–169.9), p < 0.0001] and MMP-9/NGAL [20.8 ng/ml (12.1–26.5) vs. 53.7 (27.4–73.4), p = 0.007] in diabetics and reduced leukocyte infiltration in carotid lesions of diabetics. Conclusions Higher NGAL levels in serum and plaques are associated with T2DM in patients with CAS. Metformin significantly reduced the inflammatory burden including NGAL in diabetics. Early treatment of these patients may be recommended, as elevated NGAL levels were linked with vulnerable plaques prone for embolization