1,526 research outputs found
Resistance through literature in Romania (1945-1989)
This thesis analyses how literature, as a form of cultural resistance, offered a small margin of freedom to people in communist Romania. The study is specifically concerned with the intellectual and psychological survival within the Romanian totalitarian system maintained through oppression and arbitrary exercise of power, while prohibiting any manifestation of civil and political rights. Literary production, as a form of contesting the totalitarian regime in Romania, was one of the fewest outlets that allowed the Romanian people to experience freedom within a world dominated by an enormous and ubiquitous apparatus of total control, propaganda and indoctrination. This study uses qualitative research through textual analysis of different literary genres (fictional and non-fictional prose, poetry and children\u27s literature) and the role of literature in producing a discourse that contested the totalitarian regime in which the literature of resistance developed. In order to explain resistance through literature in communist Romania, the present research also includes a discussion of resistance concept, a historical account of communism in Romania as well as the construction of the totalitarian system. By identifying instances of cultural resistance against the regime\u27s policies of total control, this thesis aims to show how writings produced under totalitarian rule can offer to authors and readership alike, the opportunity to experience freedom under extreme conditions
Bulk Spin-Hall Effect
We show that a two-dimensional spin-orbit-coupled system in the presence of a
charge/spin-density wave with a wave-vector perpendicular to an applied
electric field supports bulk manifestations of the direct/inverse spin-Hall
effect. We develop a theory of this phenomenon in the framework of the spin
diffusion equation formalism and show that, due to the inhomogeneity created by
a spin-grating, an anomalous bulk charge-density wave is induced away from
sample boundaries. The optimal conditions for the observation of the effect are
determined. The main experimental manifestation of the bulk spin-Hall effect,
the induced charge/spin-density-wave, is characterized by a pi/2-phase shift
relative to the initial non-homogeneous spin/charge-polarization profile and
has a non-monotonic time-varying amplitude.Comment: 4 pages, 4 figure
Non-equilibrium spin dynamics in a trapped Fermi gas with effective spin-orbit interaction
We consider a trapped atomic system in the presence of spatially varying
laser fields. The laser-atom interaction generates a pseudospin degree of
freedom (referred to simply as spin) and leads to an effective spin-orbit
coupling for the fermions in the trap. Reflections of the fermions from the
trap boundaries provide a physical mechanism for effective momentum relaxation
and non-trivial spin dynamics due to the emergent spin-orbit coupling. We
explicitly consider evolution of an initially spin-polarized Fermi gas in a
two-dimensional harmonic trap and derive non-equilibrium behavior of the spin
polarization. It shows periodic echoes with a frequency equal to the harmonic
trapping frequency. Perturbations, such as an asymmetry of the trap, lead to
the suppression of the spin echo amplitudes. We discuss a possible experimental
setup to observe spin dynamics and provide numerical estimates of relevant
parameters.Comment: 5 pages, 4 figures; published versio
Every graph occurs as an induced subgraph of some hypohamiltonian graph
We prove the titular statement. This settles a problem of Chvátal from 1973 and encompasses earlier results of Thomassen, who showed it for K_3, and Collier and Schmeichel, who proved it for bipartite graphs. We also show that for every outerplanar graph there exists a planar hypohamiltonian graph containing it as an induced subgraph
Artificial Intelligence for Drug Discovery: Are We There Yet?
Drug discovery is adapting to novel technologies such as data science,
informatics, and artificial intelligence (AI) to accelerate effective treatment
development while reducing costs and animal experiments. AI is transforming
drug discovery, as indicated by increasing interest from investors, industrial
and academic scientists, and legislators. Successful drug discovery requires
optimizing properties related to pharmacodynamics, pharmacokinetics, and
clinical outcomes. This review discusses the use of AI in the three pillars of
drug discovery: diseases, targets, and therapeutic modalities, with a focus on
small molecule drugs. AI technologies, such as generative chemistry, machine
learning, and multi-property optimization, have enabled several compounds to
enter clinical trials. The scientific community must carefully vet known
information to address the reproducibility crisis. The full potential of AI in
drug discovery can only be realized with sufficient ground truth and
appropriate human intervention at later pipeline stages.Comment: 30 pages, 4 figures, 184 reference
Spin relaxation in a generic two-dimensional spin-orbit coupled system
We study the relaxation of a spin density injected into a two-dimensional
electron system with generic spin-orbit interactions. Our model includes the
Rashba as well as linear and cubic Dresselhaus terms. We explicitly derive a
general spin-charge coupled diffusion equation. Spin diffusion is characterized
by just two independent dimensionless parameters which control the interplay
between different spin-orbit couplings. The real-time representation of the
diffuson matrix (Green's function of the diffusion equation) is evaluated
analytically. The diffuson describes space-time dynamics of the injected spin
distribution. We explicitly study two regimes: The first regime corresponds to
negligible spin-charge coupling and is characterized by standard charge
diffusion decoupled from the spin dynamics. It is shown that there exist
several qualitatively different dynamic behaviors of the spin density, which
correspond to various domains in the spin-orbit coupling parameter space. We
discuss in detail a few interesting phenomena such as an enhancement of the
spin relaxation times, real space oscillatory dynamics, and anisotropic
transport. In the second regime, we include the effects of spin-charge
coupling. It is shown that the spin-charge coupling leads to an enhancement of
the effective charge diffusion coefficient. We also find that in the case of
strong spin-charge coupling, the relaxation rates formally become complex and
the spin/charge dynamics is characterized by real time oscillations. These
effects are qualitatively similar to those observed in spin-grating experiments
[Weber et al., Nature 437, 1330 (2005)].Comment: 18 pages, 7 figure
Convergence towards linear combinations of chi-squared random variables: a Malliavin-based approach
We investigate the problem of finding necessary and sufficient conditions for
convergence in distribution towards a general finite linear combination of
independent chi-squared random variables, within the framework of random
objects living on a fixed Gaussian space. Using a recent representation of
cumulants in terms of the Malliavin calculus operators (introduced
by Nourdin and Peccati in \cite{n-pe-3}), we provide conditions that apply to
random variables living in a finite sum of Wiener chaoses. As an important
by-product of our analysis, we shall derive a new proof and a new
interpretation of a recent finding by Nourdin and Poly \cite{n-po-1},
concerning the limiting behaviour of random variables living in a Wiener chaos
of order two. Our analysis contributes to a fertile line of research, that
originates from questions raised by Marc Yor, in the framework of limit
theorems for non-linear functionals of Brownian local times
Optimal time-domain moment matching with partial placement of poles and zeros
In this paper we consider a minimal, linear, time-invariant (LTI) system of order n, large. Our goal is to compute an approximation of order ν < n that simultaneously matches ν moments, has ℓ poles and k zeros fixed, with ℓ + k < ν, and achieves minimal H2 norm of the approximation error. For this, in the family of ν order parametrized models that match ν moments we impose ℓ+k linear constraints yielding a subfamily of models with ℓ poles and k zeros imposed. Then, in the subfamily of ν order models matching ν moments, with ℓ poles and k zeros imposed we propose an optimization problem that provides the model yielding the minimal H2-norm of the approximation error. We analyze the first-order optimality conditions of this optimization problem and compute explicitly the gradient of the objective function in terms of the controllability and the observability Gramians of the error system. We then propose a gradient method that finds the (optimal) stable model, with fixed ℓ poles and k zeros
Surface states, Friedel oscillations, and spin accumulation in p-doped semiconductors
We consider a hole-doped semiconductor with a sharp boundary and study the
boundary spin accumulation in response to a charge current. First, we solve
exactly a single-particle quantum mechanics problem described by the isotropic
Luttinger model in half-space and construct an orthonormal basis for the
corresponding Hamiltonian. It is shown that the complete basis includes two
types of eigenstates. The first class of states contains conventional incident
and reflected waves, while the other class includes localized surface states.
Second, we consider a many-body system in the presence of a charge current
flowing parallel to the boundary. It is shown that the localized states
contribute to spin accumulation near the surface. We also show that the spin
density exhibits current-induced Friedel oscillations with three different
periods determined by the Fermi momenta of the light and heavy holes. We find
an exact asymptotic expression for the Friedel oscillations far from the
boundary. We also calculate numerically the spin density profile and compute
the total spin accumulation, which is defined as the integral of the spin
density in the direction perpendicular to the boundary. The total spin
accumulation is shown to fit very well the simple formula S ~(1 - m_L/m_H)^2,
where m_L and m_H are the light- and heavy-hole masses. The effects of disorder
are discussed. We estimate the spin relaxation time in the Luttinger model and
argue that spin physics cannot be described within the diffusion approximation.Comment: 22 pages, 8 color figure
Nanostructured thermoelectric generator for energy harvesting
This paper presents the development processes towards a new generation of nanostructured thermoelectric generators for power harvesting from small temperature gradients by using a combination of traditional silicon microfabrication techniques, electroplating and submicron ion-track nanolithography. Polyimide nanotemplates with pore diameters ranging from 30nm to 120 nm were fabricated. Preliminary results for Bi2Te3 nanowires (50 and 120 nm diameter) electroplated into polycarbonate ion-track commercial membranes are presented. Bi2Te3 nanowires of R ̄ 3m structure, with preferential orientation in the (015) and (110) crystallographic plans with nearly stoichiometric composition were electroplated. The fine-grained observed microstructure (6-10 nm) and (110) crystalline orientation appear extremely promising for improving thermoelectric material properties
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