963 research outputs found
Radiocarbon dates from the Oxford AMS system: archaeometry datelist 35
This is the 35th list of AMS radiocarbon determinations measured at the Oxford Radiocarbon Accelerator Unit (ORAU). Amongst some of the sites included here are the latest series of determinations from the key sites of Abydos, El Mirón, Ban Chiang, Grotte de Pigeons (Taforalt), Alepotrypa and Oberkassel, as well as others dating to the Palaeolithic, Mesolithic and later periods. Comments on the significance of the results are provided by the submitters of the material
Discrete Razumikhin-type technique and stability of the Euler-Maruyama method to stochastic functional differential equations
A discrete stochastic Razumikhin-type theorem is established to investigate whether the Euler--Maruyama (EM) scheme can reproduce the moment exponential stability of exact solutions of stochastic functional differential equations (SFDEs). In addition, the Chebyshev inequality and the Borel-Cantelli lemma are applied to show the almost sure stability of the EM approximate solutions of SFDEs. To show our idea clearly, these results are used to discuss stability of numerical solutions of two classes of special SFDEs, including stochastic delay differential equations (SDDEs) with variable delay and stochastically perturbed equations
RADIOCARBON AND STABLE ISOTOPE EVIDENCE OF DIETARY CHANGE FROM THE MESOLITHIC TO THE MIDDLE AGES IN THE IRON GATES: NEW RESULTS FROM LEPENSKI VIR
This is the published version, also available here: https://journals.uair.arizona.edu/index.php/radiocarbon/article/view/4269.A previous radiocarbon dating and stable isotope study of directly associated ungulate and human bone samples from Late Mesolithic burials at Schela Cladovei in Romania established that there is a freshwater reservoir effect of approximately 500 yr in the Iron Gates reach of the Danube River valley in southeast Europe. Using the d15N values as an indicator of the percentage of freshwater protein in the human diet, the 14C data for 24 skeletons from the site of Lepenski Vir were corrected for this reservoir effect. The results of the paired 14C and stable isotope measurements provide evidence of substantial dietary change over the period from about 9000 BP to about 300 BP. The data from the Early Mesolithic to the Chalcolithic are consistent with a 2-component dietary system, where the linear plot of isotopic values reflects mixing between the 2 end-members to differing degrees. Typically, the individuals of Mesolithic age have much heavier d15N signals and slightly heavier d13C, while individuals of Early Neolithic and Chalcolithic age have lighter d15N and d13C values. Contrary to our earlier suggestion, there is no evidence of a substantial population that had a transitional diet midway between those that were characteristic of the Mesolithic and Neolithic. However, several individuals with Final Mesolithic 14C ages show d15N and d13C values that are similar to the Neolithic dietary pattern. Provisionally, these are interpreted either as incomers who originated in early farming communities outside the Iron Gates region or as indigenous individuals representing the earliest Neolithic of the Iron Gates. The results from Roman and Medieval age burials show a deviation from the linear function, suggesting the presence of a new major dietary component containing isotopically heavier carbon. This is interpreted as a consequence of the introduction of millet into the human food chain
A note on "symmetric" vielbeins in bimetric, massive, perturbative and non perturbative gravities
We consider a manifold endowed with two different vielbeins
and corresponding to two different metrics and
. Such a situation arises generically in bimetric or massive
gravity (including the recently discussed version of de Rham, Gabadadze and
Tolley), as well as in perturbative quantum gravity where one vielbein
parametrizes the background space-time and the other the dynamical degrees of
freedom. We determine the conditions under which the relation can be
imposed (or the "Deser-van Nieuwenhuizen" gauge chosen). We clarify and correct
various statements which have been made about this issue.Comment: 20 pages. Section 7, prop. 6 and 7. added. Some results made more
precis
Effects of Training and Testosterone on Muscle-Fiber Types and Locomotor Performance in Male Six-Lined Racerunners (\u3cem\u3eAspidoscelis sexlineata\u3c/em\u3e)
Testosterone (T) is thought to affect a variety of traits important for fitness, including coloration, the size of sexual ornaments, aggression, and locomotor performance. Here, we investigated the effects of experimentally elevated T and locomotor training on muscle physiology and running performance in a nonterritorial male lizard species (Aspidoscelis sexlineata). Additionally, several morphological attributes were quantified to examine other characters that are likely affected by T and/or a training regimen. Neither training alone nor training with T supplementation resulted in increased locomotor performance. Instead, we found that T and training resulted in a decrease in each of three locomotor performance variables as well as in hematocrit, ventral coloration, and testis size. Strikingly, neither the size nor the fiber composition of the iliofibularis or gastrocnemius muscles was different among the two treatments or a group of untrained control animals. Hence, the relationships among T, training, and associated characters are not clear. Our results offer important insights for those hoping to conduct laboratory manipulations on nonmodel organisms and highlight the challenges of studying both training effects and the effects of steroid hormones on locomotor performance
Complexity of multilevel Monte Carlo tau-Leaping
Tau-leaping is a popular discretization method for generating approximate
paths of continuous time, discrete space, Markov chains, notably for
biochemical reaction systems. To compute expected values in this context, an
appropriate multilevel Monte Carlo form of tau-leaping has been shown to
improve efficiency dramatically. In this work we derive new analytic results
concerning the computational complexity of multilevel Monte Carlo tau-leaping
that are significantly sharper than previous ones. We avoid taking asymptotic
limits, and focus on a practical setting where the system size is large enough
for many events to take place along a path, so that exact simulation of paths
is expensive, making tau-leaping an attractive option. We use a general scaling
of the system components that allows for the reaction rate constants and the
abundances of species to vary over several orders of magnitude, and we exploit
the random time change representation developed by Kurtz. The key feature of
the analysis that allows for the sharper bounds is that when comparing relevant
pairs of processes we analyze the variance of their difference directly rather
than bounding via the second moment. Use of the second moment is natural in the
setting of a diffusion equation, where multilevel was first developed and where
strong convergence results for numerical methods are readily available, but is
not optimal for the Poisson-driven jump systems that we consider here. We also
present computational results that illustrate the new analysis.Comment: 24 pages and 2 figures. Minor edits since last versio
On constrained Langevin equations and (bio)chemical reaction networks
Stochastic effects play an important role in modeling the time evolution of chemical reaction systems in fields such as systems biology, where the concentrations of some constituent molecules can be low. The most common stochastic models for these systems are continuous time Markov chains, which track the molecular abundance of each chemical species. Often, these stochastic models are studied by computer simulations, which can quickly become computationally expensive. A common approach to reduce computational effort is to approximate the discrete valued Markov chain by a continuous valued diffusion process. However, existing diffusion approximations either do not respect the constraint that chemical concentrations are never negative (linear noise approximation) or are typically only valid until the concentration of some chemical species first becomes zero (chemical Langevin equation). In this paper, we propose (obliquely) reflected diffusions, which respect the non-negativity of chemical concentrations, as approximations for Markov chain models of chemical reaction networks. These reflected diffusions satisfy “constrained Langevin equations,” in that they behave like solutions of chemical Langevin equations in the interior of the positive orthant and are constrained to the orthant by instantaneous oblique reflection at the boundary. To motivate their form, we first illustrate our constrained Langevin approximations for two simple examples. We then describe the general form of our proposed approximation. We illustrate the performance of our approximations through comparison of their stationary distributions for the two examples with those of the Markov chain model and through simulations of more complex examples
Analytical study of non-linear transport across a semiconductor-metal junction
In this paper we study analytically a one-dimensional model for a
semiconductor-metal junction. We study the formation of Tamm states and how
they evolve when the semi-infinite semiconductor and metal are coupled
together. The non-linear current, as a function of the bias voltage, is studied
using the non-equilibrium Green's function method and the density matrix of the
interface is given. The electronic occupation of the sites defining the
interface has strong non-linearities as function of the bias voltage due to
strong resonances present in the Green's functions of the junction sites. The
surface Green's function is computed analytically by solving a quadratic matrix
equation, which does not require adding a small imaginary constant to the
energy. The wave function for the surface states is given
Performance Analysis of Effective Methods for Solving Band Matrix SLAEs after Parabolic Nonlinear PDEs
This paper presents an experimental performance study of implementations of
three different types of algorithms for solving band matrix systems of linear
algebraic equations (SLAEs) after parabolic nonlinear partial differential
equations -- direct, symbolic, and iterative, the former two of which were
introduced in Veneva and Ayriyan (arXiv:1710.00428v2). An iterative algorithm
is presented -- the strongly implicit procedure (SIP), also known as the Stone
method. This method uses the incomplete LU (ILU(0)) decomposition. An
application of the Hotelling-Bodewig iterative algorithm is suggested as a
replacement of the standard forward-backward substitutions. The upsides and the
downsides of the SIP method are discussed. The complexity of all the
investigated methods is presented. Performance analysis of the implementations
is done using the high-performance computing (HPC) clusters "HybriLIT" and
"Avitohol". To that purpose, the experimental setup and the results from the
conducted computations on the individual computer systems are presented and
discussed.Comment: 10 pages, 2 figure
From density-matrix renormalization group to matrix product states
In this paper we give an introduction to the numerical density matrix
renormalization group (DMRG) algorithm, from the perspective of the more
general matrix product state (MPS) formulation. We cover in detail the
differences between the original DMRG formulation and the MPS approach,
demonstrating the additional flexibility that arises from constructing both the
wavefunction and the Hamiltonian in MPS form. We also show how to make use of
global symmetries, for both the Abelian and non-Abelian cases.Comment: Numerous small changes and clarifications, added a figur
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