249 research outputs found
Calorons and BPS monopoles with non-trivial holonomy in the confinement phase of SU(2) gluodynamics
With the help of the cooling method applied to SU(2) lattice gauge theory at
non-zero we present numerical evidence for the existence of
superpositions of Kraan-van Baal caloron (or BPS monopole pair) solutions with
non-trivial holonomy, which might constitute an important contribution to the
semi-classical approximation of the partition function.Comment: 3 pages, 6 figures, contribution to Lattice2002(topology
Continuous representability of interval orders: The topological compatibility setting
In this paper, we go further on the problem of the continuous numerical representability
of interval orders defined on topological spaces. A new condition of compatibility between
the given topology and the indifference associated to the main trace of an interval order
is introduced. Provided that this condition is fulfilled, a semiorder has a continuous
interval order representation through a pair of continuous real-valued functions. Other
necessary and sufficient conditions for the continuous representability of interval orders
are also discussed, and, in particular, a characterization is achieved for the particular
case of interval orders defined on a topological space of finite support
Persistence of Quantum Information
There is an increasing interest in the role of macroscopic environments to
our understanding of the basics of quantum theory. The knowledge of the
implications of the quantum theory to other theories, especially to the
statistical mechanics and the domain of validity has captivated scientists from
the beginning of quantum description. In such a context, the presence of an
environment is commonly thought as entanglement, decohering and mixing
properties of quantum system. Generically, an environment is assumed to be a
noisy reservoir or a heat bath. Whereas in common interpretation of statistical
mechanics the heat bath is unspecified, in quantum systems a heat bath can also
provide an indirect interaction between otherwise totally decoupled subsystems
and consequently a means to entangle them \cite{cdkl,dvclp,bfp}. In simple
example for the entanglement between two qubits due to the interaction with a
common heat bath has been explicitly shown in \cite{b}. Whereas in that paper
the bath is described by a collection of harmonic oscillators, it seems to be
more reasonable to specify the bath by stochastic forces represented by
stochastic fields. From a more general point of view we expect the bath should
be better described in a stochastic manner and not by deterministic forces. In
the present paper we consider a two level system (qubits) which are able to
perform flip processes by a coupling to classical stochastic fields. Thus we
bridge the gap between quantum and classical probability theory. This problem
is related to many other questions of quantum optics and quantum electronics
where quantum statistical aspects arising from the intrinsic quantum character
of the system while the possible time-dependence of system parameters may be
interpreted as the influence of classical thermal fluctuations.Comment: 5 page
Cationic gemini Surfactants based on tartaric acid: Synthesis, aggregation, monolayer behaviour, and interaction with DNA
Contains fulltext :
13999.pdf (publisher's version ) (Open Access
The Schr\"odinger Functional for Improved Gluon and Quark Actions
The Schr\"odinger Functional (quantum/lattice field theory with Dirichlet
boundary conditions) is a powerful tool in the non-perturbative improvement and
for the study of other aspects of lattice QCD. Here we adapt it to improved
gluon and quark actions, on isotropic as well as anisotropic lattices.
Specifically, we describe the structure of the boundary layers, obtain the
exact form of the classically improved gauge action, and outline the
modifications necessary on the quantum level. The projector structure of
Wilson-type quark actions determines which field components can be specified at
the boundaries. We derive the form of O(a) improved quark actions and describe
how the coefficients can be tuned non-perturbatively. There is one coefficient
to be tuned for an isotropic lattice, three in the anisotropic case.
Our ultimate aim is the construction of actions that allow accurate
simulations of all aspects of QCD on coarse lattices.Comment: 39 pages, LaTeX, 11 embedded eps file
The Complex Degradation Mechanism of Copper Electrodes on Lead Halide Perovskites
Lead halide perovskite solar cells have reached power conversion efficiencies during the past few years that rival those of crystalline silicon solar cells, and there is a concentrated effort to commercialize them. The use of gold electrodes, the current standard, is prohibitively costly for commercial application. Copper is a promising low cost electrode material that has shown good stability in perovskite solar cells with selective contacts. Furthermore, it has the potential to be self passivating through the formation of CuI, a copper salt which is also used as a hole selective material. Based on these opportunities, we investigated the interface reactions between lead halide perovskites and copper in this work. Specifically, copper was deposited on the perovskite surface, and the reactions were followed in detail using synchrotron based and in house photoelectron spectroscopy. The results show a rich interfacial chemistry with reactions starting upon deposition and, with the exposure to oxygen and moisture, progress over many weeks, resulting in significant degradation of both the copper and the perovskite. The degradation results not only in the formation of CuI, as expected, but also in the formation of two previously unreported degradation products. The hope is that a deeper understanding of these processes will aid in the design of corrosion resistant copper based electrode
Tuning the Magnetic Response of Magnetospirillum magneticum by Changing the Culture Medium A Straightforward Approach to Improve Their Hyperthermia Efficiency
Magnetotactic bacteria Magnetospirillum magneticum AMB 1 have been cultured using three different media magnetic spirillum growth medium with Wolfe s mineral solution MSGM W , magnetic spirillum growth medium without Wolfe s mineral solution MSGM W , and flask standard medium FSM . The influence of the culture medium on the structural, morphological, and magnetic characteristics of the magnetosome chains biosynthesized by these bacteria has been investigated by using transmission electron microscopy, X ray absorption spectroscopy, and X ray magnetic circular dichroism. All bacteria exhibit similar average size for magnetosomes, 40 45 nm, but FSM bacteria present slightly longer subchains. In MSGM W bacteria, Co2 ions present in the medium substitute Fe2 ions in octahedral positions with a total Co doping around 4 5 . In addition, the magnetic response of these bacteria has been thoroughly studied as functions of both the temperature and the applied magnetic field. While MSGM W and FSM bacteria exhibit similar magnetic behavior, in the case of MSGM W, the incorporation of the Co ions affects the magnetic response, in particular suppressing the Verwey amp; 8764;105 K and low temperature amp; 8764;40 K transitions and increasing the coercivity and remanence. Moreover, simulations based on a Stoner Wolhfarth model have allowed us to reproduce the experimentally obtained magnetization versus magnetic field loops, revealing clear changes in different anisotropy contributions for these bacteria depending on the employed culture medium. Finally, we have related how these magnetic changes affect their heating efficiency by using AC magnetometric measurements. The obtained AC hysteresis loops, measured with an AC magnetic field amplitude of up to 90 mT and a frequency, f, of 149 kHz, reveal the influence of the culture medium on the heating properties of these bacteria below 35 mT, MSGM W bacteria are the best heating mediators, but above 60 mT, FSM and MSGM W bacteria give the best heating results, reaching a maximum heating efficiency or specific absorption rate SAR of SAR f amp; 8776; 12 W g 1 kHz
Cdc20 Is Critical for Meiosis I and Fertility of Female Mice
Chromosome missegregation in germ cells is an important cause of unexplained infertility, miscarriages, and congenital birth defects in humans. However, the molecular defects that lead to production of aneuploid gametes are largely unknown. Cdc20, the activating subunit of the anaphase-promoting complex/cyclosome (APC/C), initiates sister-chromatid separation by ordering the destruction of two key anaphase inhibitors, cyclin B1 and securin, at the transition from metaphase to anaphase. The physiological significance and full repertoire of functions of mammalian Cdc20 are unclear at present, mainly because of the essential nature of this protein in cell cycle progression. To bypass this problem we generated hypomorphic mice that express low amounts of Cdc20. These mice are healthy and have a normal lifespan, but females produce either no or very few offspring, despite normal folliculogenesis and fertilization rates. When mated with wild-type males, hypomorphic females yield nearly normal numbers of fertilized eggs, but as these embryos develop, they become malformed and rarely reach the blastocyst stage. In exploring the underlying mechanism, we uncover that the vast majority of these embryos have abnormal chromosome numbers, primarily due to chromosome lagging and chromosome misalignment during meiosis I in the oocyte. Furthermore, cyclin B1, cyclin A2, and securin are inefficiently degraded in metaphase I; and anaphase I onset is markedly delayed. These results demonstrate that the physiologically effective threshold level of Cdc20 is high for female meiosis I and identify Cdc20 hypomorphism as a mechanism for chromosome missegregation and formation of aneuploid gametes
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