4,168 research outputs found
Bringing Together Gravity and the Quanta
Due to its underlying gauge structure, teleparallel gravity achieves a
separation between inertial and gravitational effects. It can, in consequence,
describe the isolated gravitational interaction without resorting to the
equivalence principle, and is able to provide a tensorial definition for the
energy-momentum density of the gravitational field. Considering the conceptual
conflict between the local equivalence principle and the nonlocal uncertainty
principle, the replacement of general relativity by its teleparallel equivalent
can be considered an important step towards a prospective reconciliation
between gravitation and quantum mechanics.Comment: 9 pages. Contribution to the proceedings of the Albert Einstein
Century International Conference, Paris, 18-22 July, 200
Life cycle assessment of biogas production in small-scale household digesters in Vietnam
Small-scale household digesters have been promoted across Asia as a sustainable way of handling manure. The major advantages are that they produce biogas and reduce odor. However their disadvantages include the low recycling of nutrients, because digestate is dilute and therefore difficult to transport, and the loss of biogas as a result of cracks and the intentional release of excess biogas. In this study, life cycle assessment (LCA) methodology was used to assess the environmental impacts associated with biogas digesters in Vietnam. Handling 1,000 kg of liquid manure and 100 kg of solid manure in a system with a biogas digester reduced the impact potential from 4.4 kg carbon dioxide (CO2) equivalents to 3.2 kg CO2 equivalents compared with traditional manure management. However, this advantage could easily be compromised if digester construction is considered in the LCA or in situations where there is an excess of biogas which is intentionally released. A sensitivity analysis showed that biogas digesters could be a means of reducing global warming if methane emissions can be kept low. In terms of eutrophication, farms with biogas digesters had 3 to 4 times greater impacts. In order to make biogas digesters sustainable, methods for recycling digestates are urgently required
On the theory of the vortex state in the Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) phase
We demonstrate that the vortex state in the Fulde-Ferrell-Larkin-Ovchinnikov
(FFLO) phase may be very different depending on the field orientation relative
to the crystalline axes. We calculate numerically the upper critical field near
the tricritical point taking into account the modulation of the order parameter
along the magnetic field as well as the higher Landau levels. For s-wave
superconductors with the anisotropy described by an elliptical Fermi surface we
propose a general scheme of the analysis of the angular dependence of upper
critical field at all temperatures on the basis of the exact solution for the
order parameter. Our results show that the transitions (with tilting magnetic
field) between different types of mixed states may be a salient feature of the
FFLO phase. Moreover we discuss the reasons for the first-order phase
transition into the FFLO state in the case of CeCoIn5 compound.Comment: 7 figure
Theory of the optical absorption of light carrying orbital angular momentum by semiconductors
We develop a free-carrier theory of the optical absorption of light carrying
orbital angular momentum (twisted light) by bulk semiconductors. We obtain the
optical transition matrix elements for Bessel-mode twisted light and use them
to calculate the wave function of photo-excited electrons to first-order in the
vector potential of the laser. The associated net electric currents of first
and second-order on the field are obtained. It is shown that the magnetic field
produced at the center of the beam for the mode is of the order of a
millitesla, and could therefore be detected experimentally using, for example,
the technique of time-resolved Faraday rotation.Comment: Submitted to Phys. Rev. Lett. (23 Jan 2008
Quantum mechanics in multiply connected spaces
This paper analyses quantum mechanics in multiply connected spaces. It is
shown that the multiple connectedness of the configuration space of a physical
system can determine the quantum nature of physical observables, such as the
angular momentum. In particular, quantum mechanics in compactified Kaluza-Klein
spaces is examined. These compactified spaces give rise to an additional
angular momentum which can adopt half-integer values and, therefore, may be
identified with the intrinsic spin of a quantum particle.Comment: Latex 15 page
Clinical Applications of Heart Rate Variability in the Triage and Assessment of Traumatically Injured Patients
Heart rate variability (HRV) is a method of physiologic assessment which uses fluctuations in the RR intervals to evaluate modulation of the heart rate by the autonomic nervous system (ANS). Decreased variability has been studied as a marker of increased pathology and a predictor of morbidity and mortality in multiple medical disciplines. HRV is potentially useful in trauma as a tool for prehospital triage, initial patient assessment, and continuous monitoring of critically injured patients. However, several technical limitations and a lack of standardized values have inhibited its clinical implementation in trauma. The purpose of this paper is to describe the three analytical methods (time domain, frequency domain, and entropy) and specific clinical populations that have been evaluated in trauma patients and to identify key issues regarding HRV that must be explored if it is to be widely adopted for the assessment of trauma patients
Multiple-point statistical simulation for hydrogeological models: 3D training image development and conditioning strategies
Most studies about the application of geostatistical simulations based on multiple-point statistics (MPS) to hydrogeological modelling focus on relatively fine-scale models and concentrate on the estimation of facies-level, structural uncertainty. Much less attention is paid to the use of input data and optimal construction of training images. For instance, even though the training image should capture a set of spatial geological characteristics to guide the simulations, the majority of the research still relies on 2D or quasi-3D training images. In the present study, we demonstrate a novel strategy for 3D MPS modelling characterized by: (i) realistic 3D training images, and (ii) an effective workflow for incorporating a diverse group of geological and geophysical data sets. The study covers an area of 2810 km2 in the southern part of Denmark. MPS simulations are performed on a subset of the geological succession (the lower to middle Miocene sediments) which is characterized by relatively uniform structures and dominated by sand and clay. The simulated domain is large and each of the geostatistical realizations contains approximately 45 million voxels with size 100 m × 100 m × 5 m. Data used for the modelling include water well logs, high-resolution seismic data, and a previously published 3D geological model. We apply a series of different strategies for the simulations based on data quality, and develop a novel method to effectively create observed sand/clay spatial trends. The training image is constructed as a small 3D voxel model covering an area of 90 km2. We use an iterative training image development strategy and find that even slight modifications in the training image create significant changes in simulations. Thus, the study underlines that it is important to consider both the geological environment, and the type and quality of input information in order to achieve optimal results from MPS modelling. In this study we present a possible workflow to build the training image and effectively handle different types of input information to perform large-scale geostatistical modellin
Universal microscopic correlation functions for products of independent Ginibre matrices
We consider the product of n complex non-Hermitian, independent random
matrices, each of size NxN with independent identically distributed Gaussian
entries (Ginibre matrices). The joint probability distribution of the complex
eigenvalues of the product matrix is found to be given by a determinantal point
process as in the case of a single Ginibre matrix, but with a more complicated
weight given by a Meijer G-function depending on n. Using the method of
orthogonal polynomials we compute all eigenvalue density correlation functions
exactly for finite N and fixed n. They are given by the determinant of the
corresponding kernel which we construct explicitly. In the large-N limit at
fixed n we first determine the microscopic correlation functions in the bulk
and at the edge of the spectrum. After unfolding they are identical to that of
the Ginibre ensemble with n=1 and thus universal. In contrast the microscopic
correlations we find at the origin differ for each n>1 and generalise the known
Bessel-law in the complex plane for n=2 to a new hypergeometric kernel 0_F_n-1.Comment: 20 pages, v2 published version: typos corrected and references adde
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