Relaxation dynamics of the toric code in contact with a thermal reservoir: Finite-size scaling in a low temperature regime

We present an analysis of the relaxation dynamics of finite-size topological qubits in contact with a thermal bath. Using a continuous-time Monte Carlo method, we explicitly compute the low-temperature nonequilibrium dynamics of the toric code on finite lattices. In contrast to the size-independent bound predicted for the toric code in the thermodynamic limit, we identify a low-temperature regime on finite lattices below a size-dependent crossover temperature with nontrivial finite-size and temperature scaling of the relaxation time. We demonstrate how this nontrivial finite-size scaling is governed by the scaling of topologically nontrivial two-dimensional classical random walks. The transition out of this low-temperature regime defines a dynamical finite-size crossover temperature that scales inversely with the log of the system size, in agreement with a crossover temperature defined from equilibrium properties. We find that both the finite-size and finite-temperature scaling are stronger in the low-temperature regime than above the crossover temperature. Since this finite-temperature scaling competes with the scaling of the robustness to unitary perturbations, this analysis may elucidate the scaling of memory lifetimes of possible physical realizations of topological qubits.Comment: 14 Pages, 13 figure

Detecting the effects of selection at the population level in six bovine immune genes

<p>Abstract</p> <p>Background</p> <p>The capacity of a species or population to respond to and survive novel infectious disease challenge is one of the most significant selective forces shaping genetic diversity and the period following animal domestication was likely one of the most important in terms of newly emerging diseases. Inter-specific genome-wide comparison has suggested that genes, including cluster of differentiation 2 (CD2), ADP-ribosyltransferase 4 (ART4), tyrosine kinase binding protein (TYROBP) and interleukins IL2, IL5, IL13, may have undergone positive selection during the evolution of the bovine lineage. Past adaptive change implies that more recent variation may have also been subject to selective forces.</p> <p>Results</p> <p>In this paper, we re-sequence each of these genes in cattle cohorts from Europe, Africa and Asia to investigate patterns of polymorphism at the population level. Patterns of diversity are higher within <it>Bos indicus </it>suggesting different demographic history to that of <it>Bos taurus</it>. Significant coding polymorphism was observed within each of the cell-surface receptors. In particular, CD2 shows two divergent haplotypes defined by a series of six derived nonsynonymous substitutions that are significantly clustered on the extracellular surface of the protein and give significant values for Fay and Wu's <it>H</it>, strongly suggesting a recent adaptive history. In contrast, the signaling molecules (especially IL13) display outlying allele frequency spectra which are consistent with the effects of selection, but display negligible coding polymorphism.</p> <p>Conclusion</p> <p>We present evidence suggestive of recent adaptive history in bovine immune genes; implying some correspondence between intra- and inter-specific signals of selection. Interestingly, three signaling molecules have negligible nonsynonymous variation but show outlying test statistics in contrast to three receptors, where it is protein sequence diversity that suggests selective history.</p

TPN‐associated intestinal epithelial cell atrophy is modulated by TLR4/EGF signaling pathways

Recent studies suggest a close interaction between epidermal growth factor (EGF) and TLR signaling in the modulation of intestinal epithelial cell (IEC) proliferation; however, how these signaling pathways adjust IEC proliferation is poorly understood. We utilized a model of total parenteral nutrition (TPN), or enteral nutrient deprivation, to study this interaction as TPN results in mucosal atrophy due to decreased IEC proliferation and increased apoptosis. We identified the novel finding of decreased mucosal atrophy in TLR4 knockout (TLR4KO) mice receiving TPN. We hypothesized that EGF signaling is preserved in TLR4KO‐TPN mice and prevents mucosal atrophy. C57B1/6 and strain‐matched TLR4KO mice were provided either enteral feeding or TPN. IEC proliferation and apoptosis were measured. Cytokine and growth factor abundances were detected in both groups. To examine interdependence of these pathways, ErbB1 pharmacologic blockade was used. The marked decline in IEC proliferation with TPN was nearly prevented in TLR4KO mice, and intestinal length was partially preserved. EGF was significantly increased, and TNF‐α decreased in TLR4KO‐TPN versus wild‐type (WT)‐TPN mice. Apoptotic positive crypt cells were 15‐fold higher in WT‐TPN versus TLR4KO‐TPN mice. Bcl‐2 was significantly increased in TLR4KOTPN mice, while Bax decreased 10‐fold. ErbB1 blockade prevented this otherwise protective effect in TLR4KO‐sTPN mice. TLR4 blockade significantly prevented TPN‐associated atrophy by preserving proliferation and preventing apoptosis. This is driven by a reduction in TNF‐α abundance and increased EGF. Potential manipulation of this regulatory pathway may have significant clinical potential to prevent TPN‐associated atrophy.—Freeman, J. J., Feng, Y., Demehri, F. R., Dempsey, P. J., Teitelbaum, D. H. TPN‐associated intestinal epithelial cell atrophy is modulated by TLR4/EGF signaling pathways. FASEB J. 29, 2943‐2958 (2015). www.fasebj.orgPeer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/154328/1/fsb2fj14269480.pd

Dimensional Strategies and the Minimization Problem: Barrier-Avoiding Algorithms

In the present paper we examine the role of dimensionality in the minimization problem. Since it has such a powerful influence on the topology of the associated potential energy landscape, we argue that it may prove useful to alter the dimensionality of the space of the original minimization problem. We explore this general idea in the context of finding the minimum energy geometries of Lennard-Jones clusters. We show that it is possible to locate barrier-free, high-dimensional pathways that connect local, three-dimensional cluster minima. The performance of the resulting, “barrier-avoiding minimization” algorithm is examined for clusters containing as many as 55 atoms

Use of Dynamic Models and Operational Architecture to Solve Complex Navy Challenges

The United States Navy established 8 Maritime Operations Centers (MOC) to enhance the command and control of forces at the operational level of warfare. Each MOC is a headquarters manned by qualified joint operational-level staffs, and enabled by globally interoperable C41 systems. To assess and refine MOC staffing, equipment, and schedules, a dynamic software model was developed. The model leverages pre-existing operational process architecture, joint military task lists that define activities and their precedence relations, as well as Navy documents that specify manning and roles per activity. The software model serves as a "computational wind-tunnel" in which to test a MOC on a mission, and to refine its structure, staffing, processes, and schedules. More generally, the model supports resource allocation decisions concerning Doctrine, Organization, Training, Material, Leadership, Personnel and Facilities (DOTMLPF) at MOCs around the world. A rapid prototype effort efficiently produced this software in less than five months, using an integrated process team consisting of MOC military and civilian staff, modeling experts, and software developers. The work reported here was conducted for Commander, United States Fleet Forces Command in Norfolk, Virginia, code N5-0LW (Operational Level of War) that facilitates the identification, consolidation, and prioritization of MOC capabilities requirements, and implementation and delivery of MOC solutions

VETA-1 x ray detection system

The alignment and X-ray imaging performance of the Advanced X-ray Astrophysics Facility (AXAF) Verification Engineering Test Article-I (VETA-I) was measured by the VETA-I X-Ray Detection System (VXDS). The VXDS was based on the X-ray detection system utilized in the AXAF Technology Mirror Assembly (TMA) program, upgraded to meet the more stringent requirements of the VETA-I test program. The VXDS includes two types of X-ray detectors: (1) a High Resolution Imager (HRI) which provides X-ray imaging capabilities, and (2) sealed and flow proportional counters which, in conjunction with apertures of various types and precision translation stages, provide the most accurate measurement of VETA-I performance. Herein we give an overview of the VXDS hardware including X-ray detectors, translation stages, apertures, proportional counters and flow counter gas supply system and associated electronics. We also describe the installation of the VXDS into the Marshall Space Flight Center (MSFC) X-Ray Calibration Facility (XRCF). We discuss in detail the design and performance of those elements of the VXDS which have not been discussed elsewhere; translation systems, flow counter gas supply system, apertures and thermal monitoring system