212 research outputs found
Exact solutions of Brans-Dicke wormholes in the presence of matter
A fundamental ingredient in wormhole physics is the presence of exotic
matter, which involves the violation of the null energy condition. Although a
plethora of wormhole solutions have been explored in the literature, it is
useful to find geometries that minimize the usage of exotic matter. In this
work, we find exact wormhole solutions in Brans-Dicke theory where the normal
matter threading the wormhole satisfies the null energy condition throughout
the geometry. Thus, the latter implies that it is the effective stress-energy
tensor containing the scalar field, that plays the role of exotic matter, that
is responsible for sustaining the wormhole geometry. More specifically, we
consider a zero redshift function and a particular choice for the scalar field
and determine the remaining quantities, namely, the stress-energy tensor
components and the shape function. The solution found is not asymptotically
flat, so that this interior wormhole spacetime needs to be matched to an
exterior vacuum solution.Comment: 7 pages, 3 figure
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SI PC104 Performance Test Report
The Spectral Instruments (SI) PC104 systems associated with the SI-1000 CCD camera exhibited intermittent power problems during setup, test and operations which called for further evaluation and testing. The SI PC104 System is the interface between the SI-1000 CCD camera and its associated Diagnostic Controller (DC). As such, the SI PC104 must be a reliable, robust system capable of providing consistent performance in various configurations and operating conditions. This SI PC104 system consists of a stackable set of modules designed to meet the PC104+ Industry Standard. The SI PC104 System consists of a CPU module, SI Camera card, Media converter card, Video card and a I/O module. The root cause of power problems was identified as failing solder joints at the LEMO power connector attached to the SI Camera Card. The recommended solution was to provide power to the PC104 system via a PC104+ power supply module configured into the PC104 stack instead of thru the LEMO power connector. Test plans (2) were developed to test SI PC104 performance and identify any outstanding issues noted during extended operations. Test Plan 1 included performance and image acquisition tests. Test Plan 2 verified performance after implementing recommendations. Test Plan 2 also included verifying integrity of system files and driver installation after bootup. Each test plan was implemented to fully test against each set of problems noted. Test Plan presentations and Test Plan results are attached as appendices. Anticipated test results will show successful operation and reliable performance of the SI PC104 system receiving its power via a PC104 power supply module. A SI PC104 Usage Recommendation Memo will be sent out to the SI PC104 User Community. Recommendation memo(s) are attached as appendices
Wormhole geometries supported by a nonminimal curvature-matter coupling
Wormhole geometries in curvature-matter coupled modified gravity are
explored, by considering an explicit nonminimal coupling between an arbitrary
function of the scalar curvature, R, and the Lagrangian density of matter. It
is the effective stress-energy tensor containing the coupling between matter
and the higher order curvature derivatives that is responsible for the null
energy condition violation, and consequently for supporting the respective
wormhole geometries. The general restrictions imposed by the null energy
condition violation are presented in the presence of a nonminimal R-matter
coupling. Furthermore, obtaining exact solutions to the gravitational field
equations is extremely difficult due to the nonlinearity of the equations,
although the problem is mathematically well-defined. Thus, we outline several
approaches for finding wormhole solutions, and deduce an exact solution by
considering a linear R nonmiminal curvature-matter coupling and by considering
an explicit monotonically decreasing function for the energy density. Although
it is difficult to find exact solutions of matter threading the wormhole
satisfying the energy conditions at the throat, an exact solution is found
where the nonminimal coupling does indeed minimize the violation of the null
energy condition of normal matter at the throat.Comment: 8 pages, 3 figures. V2: 9 pages, error and typos corrected;
discussion and references added; to appear in PR
Energy conditions in modified Gauss-Bonnet gravity
In considering alternative higher-order gravity theories, one is liable to be
motivated in pursuing models consistent and inspired by several candidates of a
fundamental theory of quantum gravity. Indeed, motivations from string/M-theory
predict that scalar field couplings with the Gauss-Bonnet invariant, G, are
important in the appearance of non-singular early time cosmologies. In this
work, we discuss the viability of an interesting alternative gravitational
theory, namely, modified Gauss-Bonnet gravity or f(G) gravity. We consider
specific realistic forms of f(G) analyzed in the literature that account for
the late-time cosmic acceleration and that have been found to cure the
finite-time future singularities present in the dark energy models. We present
the general inequalities imposed by the energy conditions and use the recent
estimated values of the Hubble, deceleration, jerk and snap parameters to
examine the viability of the above-mentioned forms of f(G) imposed by the weak
energy condition.Comment: 9 pages, 8 figures. V2: minor additions and corrections; to appear in
PR
Reversible photonic hydrogel sensors via holographic interference lithography
Continuous monitoring of physiological conditions and biomarkers via optical holographic sensors is an area of growing interest to facilitate the expansion of personalised medicine. Here, a facile laser-induced dual polymerization method is developed to fabricate holographic hydrogel sensors for the continuous and reversible colorimetric determination of pH variations over a physiological range in serum (pH 7–9). Readout parameters simulated through a Finite-difference time-domain Yee's algorithm retrieve the spectral response through expansion. Laser lithography of holographic hydrogel sensor fabrication is achieved via a single 355 nm laser pulse to initiate polymerization of ultrafine hydrogel fringes. Eliminating the requirement for complex processing of toxic components and streamlining the synthetic procedure provides a simpler route to mass production. Optimised pH-responsive hydrogels contain amine bearing functional co-monomers demonstrating reversible Bragg wavelength shifts of 172 nm across the entire visible wavelength range with pH variation from 7.0 to 9.0 upon illumination with broadband light. Photolithographic recording of information shows the ability to convey detailed information to users for qualitative identification of pH. Holographic sensor reversibility over 20 cycles showed minimal variation in replay wavelength supporting reliable and consistent readout, with optimised sensors showing rapid response times of <5 min. The developed sensors demonstrate the application to continuous monitoring in biological fluids, withstanding interference from electrolytes, saccharides, and proteins colorimetrically identifying bovine serum pH over a physiological range. The holographic sensors benefit point-of-care pH analysis of biological analytes which could be applied to the identification of blood gas disorders and wound regeneration monitoring through colorimetric readouts
Characterization of the chemical composition of banana peels from southern Brazil across the seasons using nuclear magnetic resonance and chemometrics
Banana peels are a source of important bioactive compounds, such as phenolics, carotenoids, biogenic amines, among others. For industrial usage of that by-product, a certain homogeneity of its chemical composition is claimed, a trait affected by the effect of (a)bioatic ecological factors. In this sense, this study aimed to investigate the banana peels chemical composition, to get insights on eventual metabolic changes caused by the seasons, in southern Brazil. For this purpose, a Nuclear Magnetic Resonance (NMR)-based metabolic profiling strategy was adopted, followed by chemometrics analysis, using the specmine package for the R environment. The obtained results show that the different seasons can, in fact, influence the metabolic composition, namely the levels of metabolites extracted from the bananas peels. The analytical approach herein adopted, i.e., NMR-based metabolomics coupled to chemometrics analysis, seems to enable identifying the chemical heterogeneity of banana peels over the harvest seasons, allowing obtaining standardized extracts for further technological purposes of usage.CAPES -Coordenação de Aperfeiçoamento de Pessoal de NÃvel Superior(407323/2013-9)info:eu-repo/semantics/publishedVersio
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