3,740 research outputs found
Hawking Radiation in String Theory and the String Phase of Black Holes
The quantum string emission by Black Holes is computed in the framework of
the `string analogue model' (or thermodynamical approach), which is well suited
to combine QFT and string theory in curved backgrounds (particulary here, as
black holes and strings posses intrinsic thermal features and temperatures).
The QFT-Hawking temperature T_H is upper bounded by the string temperature T_S
in the black hole background. The black hole emission spectrum is an incomplete
gamma function of (T_H - T_S). For T_H << T_S, it yields the QFT-Hawking
emission. For T_H \to T_S, it shows highly massive string states dominate the
emission and undergo a typical string phase transition to a microscopic
`minimal' black hole of mass M_{\min} or radius r_{\min} (inversely
proportional to T_S) and string temperature T_S. The semiclassical QFT black
hole (of mass M and temperature T_H) and the string black hole (of mass M_{min}
and temperature T_S) are mapped one into another by a `Dual' transform which
links classical/QFT and quantum string regimes. The string back reaction effect
(selfconsistent black hole solution of the semiclassical Einstein equations
with mass M_+ (radius r_+) and temperature T_+) is computed. Both, the QFT and
string black hole regimes are well defined and bounded: r_{min} leq r_+ \leq
r_S, M_{min} \leq M_+ \leq M, T_H \leq T_+ \leq T_S. The string `minimal' black
hole has a life time tau_{min} \simeq \frac{k_B c}{G \hbar} T^{-3}_S.Comment: LaTex, 31 pages, no figure
El Buddhisme i la medicina de l'esperit
En aquest article, el professor Ramon N. Prats, especialista en budisme, posa de manifest la relaciĂł que existeix entre aquesta saviesa oriental i les religions occidentals. Seguint alguns pensaments del Dalai Lama, el professor Prats investiga les possibilitats reals d'un diĂ leg interreligiĂłs des del budisme
System Design and Control Optimization for Neurorehabilitation Exoskeleton
Neurorehabilitation is a comprehensive approach aimed at helping patients regain motor control after a neural injury, including spinal cord injury, stroke, or other ischemic events. Early-stage neurorehabilitation is particularly delicate due to voluntary muscular weakness and lack of motor control, presenting in the form of spasticity. Unfortunately, this period of elevated weakness is when most neural control improvement can be made through a phenomenon called brain plasticity. Early rehabilitation traditionally requires a human therapist due to the adaptive and dynamic interpretation of undesired neuromuscular events. While efforts have been made to develop devices to aid in neurorehabilitation, the considerations that must be taken into account to design and develop an applicable, effective, and safe device can become a hindrance, preventing the proliferation of devices that could affect positive change in the communities that require them. Considerations for a neurorehabilitation device include sensor placement and usage, mechanical design, control system and design, physical interfacing, and user experience. In the following work, we first explore the physical design and development of an exoskeleton-type device, funded by the Department of Energy, that provides active assistive support to users and is therefore adaptable for early-stage neurorehabilitation patients. This device is capable of singular joint movement using a position-following controller with a manual interface. We employed serial elastic actuating modalities to stabilize displacement sensations and provided joint space feedback required for accurate displacement. We further include an analysis into control efficacy, wherein the average settling time for the position-based algorithm was of 2.02s, and the velocity algorithm performed at 3.04s. In terms of accuracy, the users were able to reach the desired positions within the 10 second time limit with 81% and 73% accuracy for the position control and velocity control, respectively. Following, we explore control mechanisms applicable to rehabilitative devices and define an admittance controller. We conclude parameterized control using biomechanical signals in an exoskeleton-type is viable, and including a feed-forward loop in the admittance controller provides the most coupled stability in the system following marginal analyses
Optical properties of apple skin and flesh in the wavelength range from 350 to 2200 nm
Optical measurement of fruit quality is challenging due to the presence of a skin around the fruit flesh and the multiple scattering by the structured tissues. To gain insight in the light-tissue interaction, the optical properties of apple skin and flesh tissue are estimated in the 350-2200nm range for three cultivars. For this purpose, single integrating sphere measurements are combined with inverse adding- doubling. The observed absorption coefficient spectra are dominated by water in the near infrared and by pigments and chlorophyll in the visible region, whose concentrations are much higher in skin tissue. The scattering coefficient spectra show the monotonic decrease with increasing wavelength typical for biological tissues with skin tissue being approximately three times more scattering than flesh tissue. Comparison to the values from time-resolved spectroscopy reported in literature showed comparable profiles for the optical properties, but overestimation of the absorption coefficient values, due to light losses
Strategies to enhance the 3T1D-DRAM cell variability robustness beyond 22 nm
3T1D cell has been stated as a valid alternative to be implemented on L1 memory cache to substitute 6T, highly affected by device variability as technology dimensions are reduced. In this work, we have shown that 22 nm 3T1D memory cells present significant tolerance to high levels of device parameter fluctuation. Moreover, we have observed that when variability is considered the write access transistor becomes a significant detrimental element on the 3T1D cell performance. Furthermore, resizing and temperature control have been presented as some valid strategies in order to mitigate the 3T1D cell variability.Peer ReviewedPostprint (author's final draft
Stochastic theory of large-scale enzyme-reaction networks: Finite copy number corrections to rate equation models
Chemical reactions inside cells occur in compartment volumes in the range of
atto- to femtolitres. Physiological concentrations realized in such small
volumes imply low copy numbers of interacting molecules with the consequence of
considerable fluctuations in the concentrations. In contrast, rate equation
models are based on the implicit assumption of infinitely large numbers of
interacting molecules, or equivalently, that reactions occur in infinite
volumes at constant macroscopic concentrations. In this article we compute the
finite-volume corrections (or equivalently the finite copy number corrections)
to the solutions of the rate equations for chemical reaction networks composed
of arbitrarily large numbers of enzyme-catalyzed reactions which are confined
inside a small sub-cellular compartment. This is achieved by applying a
mesoscopic version of the quasi-steady state assumption to the exact
Fokker-Planck equation associated with the Poisson Representation of the
chemical master equation. The procedure yields impressively simple and compact
expressions for the finite-volume corrections. We prove that the predictions of
the rate equations will always underestimate the actual steady-state substrate
concentrations for an enzyme-reaction network confined in a small volume. In
particular we show that the finite-volume corrections increase with decreasing
sub-cellular volume, decreasing Michaelis-Menten constants and increasing
enzyme saturation. The magnitude of the corrections depends sensitively on the
topology of the network. The predictions of the theory are shown to be in
excellent agreement with stochastic simulations for two types of networks
typically associated with protein methylation and metabolism.Comment: 13 pages, 4 figures; published in The Journal of Chemical Physic
A machine learning based framework to identify and classify long terminal repeat retrotransposons
Transposable elements (TEs) are repetitive nucleotide sequences that make up a large portion of eukaryotic genomes. They can move and duplicate within a genome, increasing genome size and contributing to genetic diversity within and across species. Accurate identification and classification of TEs present in a genome is an important step towards understanding their effects on genes and their role in genome evolution. We introduce TE-LEARNER, a framework based on machine learning that automatically identifies TEs in a given genome and assigns a classification to them. We present an implementation of our framework towards LTR retrotransposons, a particular type of TEs characterized by having long terminal repeats (LTRs) at their boundaries. We evaluate the predictive performance of our framework on the well-annotated genomes of Drosophila melanogaster and Arabidopsis thaliana and we compare our results for three LTR retrotransposon superfamilies with the results of three widely used methods for TE identification or classification: REPEATMASKER, CENSOR and LTRDIGEST. In contrast to these methods, TE-LEARNER is the first to incorporate machine learning techniques, outperforming these methods in terms of predictive performance , while able to learn models and make predictions efficiently. Moreover, we show that our method was able to identify TEs that none of the above method could find, and we investigated TE-LEARNER'S predictions which did not correspond to an official annotation. It turns out that many of these predictions are in fact strongly homologous to a known TE
Microquasars as sources of positron annihilation radiation
We consider the production of positrons in microquasars, i.e. X-ray binary
systems that exhibit jets frequently, but not continuously. We estimate the
production rate of positrons in microquasars, both by simple energy
considerations and in the framework of various proposed models. We then
evaluate the collective emissivity of the annihilation radiation produced by
Galactic microquasars and we find that it might constitute a substantial
contribution to the annihilation flux measured by INTEGRAL/SPI. We also discuss
the possible spatial distribution of Galactic microquasars, on the basis of the
(scarce) available data and the resulting morphology of the flux received on
Earth. Finally, we consider nearby 'misaligned' microquasars, with jets
occasionally hitting the atmosphere of the companion star; these would
represent interesting point sources, for which we determine the annihilation
flux and the corresponding light curve, as well as the line's spectral profile.
We discuss the possibility of detection of such point sources by future
instruments.Comment: 13 pages, 7 figures, accepted in A&
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