Chiral single-wall gold nanotubes

Based on first-principles calculations we show that gold atoms can form both free-standing and tip-suspended chiral single-wall nanotubes composed of helical atomic strands. Free-standing, infinite (5,5) tube is found to be energetically the most favorable. While energetically less favorable, the experimentally observed (5,3) tube stretching between two tips corresponds to a local minimum in the string tension. Similarly, the (4,3) tube is predicted as a favorable structure yet to be observed experimentally. Analysis of band structure, charge density, and quantum ballistic conductance suggests that the current on these wires is less chiral than expected, and there is no direct correlation between the numbers of conduction channels and helical strands.Comment: Figures provided in eps forma

Comparing hierarchies of total functionals

In this paper we consider two hierarchies of hereditarily total and continuous functionals over the reals based on one extensional and one intensional representation of real numbers, and we discuss under which asumptions these hierarchies coincide. This coincidense problem is equivalent to a statement about the topology of the Kleene-Kreisel continuous functionals. As a tool of independent interest, we show that the Kleene-Kreisel functionals may be embedded into both these hierarchies.Comment: 28 page

Application of different models to the lactation curves of unimproved Awassi ewes in Turkey

The objective of this study was to investigate the use of four different mathematical functions (Wood, Inverse Polynomial, Quadratic and Cubic models) for describing the lactation curve of unimproved Awassi ewes. Data were collected from 136 ewes from the same flock raised on the State Farm of Gözlü in the Konya Province of Turkey. The differences in estimated total milk yields between the models were not statistically significant. All models were adequate in describing total milk yield, though total milk yield estimated using the Cubic model was very close to total milk yield calculated by the Fleischmann method. Age effects on model parameters were not significant. The Inverse Polynomial model overestimated the peak yield significantly. Estimated peak yields of the Wood and Cubic model were similar while that obtained from the Quadratic model was significantly lower than that of the other models. Day of peak yield estimated by the models varied between 10.2 and 56.4 days. The differences between days of peak yield estimated using the different models were significant. R2 values of the models ranged from 0.724 to 0.977. The Cubic model gave the best R2 value. The lowest mean square prediction error was found using the Cubic model. Correlation coefficients between total milk yield calculated by the Fleischmann method and estimated total milk yield from the other models ranged from 0.933 to 0.998. The highest correlation coefficient was found for the Cubic model. As a result, the Cubic model showed the best fit to the data collected from unimproved Awassi ewes and allowed a suitable description of the shape of the lactation curve. South African Journal of Animal Science Vol. 35(4) 2005: 238-24

Ab-initio electron transport calculations of carbon based string structures

First-principles calculations show that monatomic strings of carbon have high cohesive energy and axial strength, and exhibit stability even at high temperatures. Due to their flexibility and reactivity, carbon chains are suitable for structural and chemical functionalizations; they form also stable ring, helix, grid and network structures. Analysis of electronic conductance of various infinite, finite and doped string structures reveal fundamental and technologically interesting features. Changes in doping and geometry give rise to dramatic variations in conductance. In even-numbered linear chains strain induces substantial decrease of conductance. The double covalent bonding of carbon atoms underlies their unusual chemical, mechanical and transport properties.Comment: 4 pages, 4 figure

Operating System Support for Mobile Agents

An "agent" is a process that may migrate through a computer network in order to satisfy requests made by its clients. Agents implement a computational metaphor that is analogous to how most people conduct business in their daily lives: visit a place, use a service (perhaps after some negotiation), and then move on. Thus, for the computer illiterate, agents are an attractive way to describe network-wide computations. Agents are also useful abstractions for programmers who must implement distributed applications. This is because in the agent metaphor, the processor or "place" the computation is performed is not hidden from the programmer, but the communications channels are. Most current research on agents has focused on language design and application issues. The TACOMA project (Tromso And COrnell Moving Agents) has, instead, focused on operating system support for agents and how agents can be used to solve problems traditionally addressed by operating systems. We have implemented prototype systems to support agents using UNIX and using Tcl/Tk on top of Horus. This paper outlines insights and questions based on that experience. We discuss abstractions needed by an operating system to support agents, and discuss some problems that arise in connection with electronic commerce involving agents

An introduction to the TACOMA distributed system. Version 1.0

This report briefly introduces TACOMA Version 1.0. This distributed system supports agents, computations that can roam the internet. The report presents the TACOMA project, the computational model, how to get started, and the basic TACOMA abstractions

Hospital- and patient-related factors associated with differences in hospital antibiotic use: analysis of national surveillance results

Background Surveillance data of antibiotic use are increasingly being used for benchmarking purposes, but there is a lack of studies dealing with how hospital- and patient-related factors affect antibiotic utilization in hospitals. Our objective was to identify factors that may contribute to differences in antibiotic use. Methods Based on pharmacy sales data (2006–2011), use of all antibiotics, all penicillins, and broad-spectrum antibiotics was analysed in 22 Health Enterprises (HEs). Antibiotic utilization was measured in World Health Organisation defined daily doses (DDDs) and hospital-adjusted (ha)DDDs, each related to the number of bed days (BDs) and the number of discharges. For each HE, all clinical specialties were included and the aggregated data at the HE level constituted the basis for the analyses. Fourteen variables potentially associated with the observed antibiotic use – extracted from validated national databases – were examined in 12 multiple linear regression models, with four different measurement units: DDD/100 BDs, DDD/100 discharges, haDDD/100 BDs and haDDD/100 discharges. Results Six variables were independently associated with antibiotic use, but with a variable pattern depending on the regression model. High levels of nurse staffing, high proportions of short (10 days) hospital stays, infectious diseases being the main ICD-10 diagnostic codes, and surgical diagnosis-related groups were correlated with a high use of all antibiotics. University affiliated HEs had a lower level of antibiotic utilization than other institutions in eight of the 12 models, and carried a high explanatory strength. The use of broad-spectrum antibiotics correlated strongly with short and long hospital stays. There was a residual variance (30%–50% for all antibiotics; 60%–70% for broad-spectrum antibiotics) that our analysis did not explain. Conclusions The factors associated with hospital antibiotic use were mostly non-modifiable. By adjusting for these factors, it will be easier to evaluate and understand observed differences in antibiotic use between hospitals. Consequently, the inter-hospital differences can be more confidently acted upon. The residual variation is presumed to largely reflect prescriber-related factors

Early postpartum lactation effects of cesarean and vaginal birth

Objectives: Breastfeeding has positive effects for both, the mother and the infant. The purpose of the study was to ex­amine how cesarean delivery and vaginal delivery influenced subsequent breastfeeding. The study was conducted at the Kırıkkale University Medical School. Material and methods: Breastfeeding outcomes after an elective cesarean delivery and after a planned vaginal delivery were compared. The study included 169 consenting mothers who gave birth to healthy infants (86 cesarean deliveries and 83 vaginal deliveries) between March and September 2001. All cesarean deliveries were performed under regional anesthesia. Results: Elective cesarean delivery was performed at a significantly earlier gestational age as compared to vaginal delivery (p = 0.001). Maternal age in the planned vaginal delivery group was significantly lower (p = 0.003). As for the change in prolactin levels, the results were similar but not statistically significant (p = 0.21). The frequency of breastfeeding per day did not differ significantly between the groups (p = 0.20). However, women after cesarean delivery tended to breastfeed more often than after vaginal delivery (p = 0.003). Mean number of points recorded at the first breastfeeding session, according to the LATCH charting system, was lower in the group after cesarean delivery as compared to vaginal labor. The difference between the average point scores of vaginal delivery and cesarean delivery mothers was found to be meaningful in favor of the women after vaginal delivery (p = 0.05). Conclusions: Elective cesarean section has negative effects on breastfeeding. Our results indicate that cesarean section constitutes a risk factor for delayed lactogenesis

Many-body quantum chaos in stroboscopically-driven cold atoms

Seeking signatures of quantum chaos in experimentally realizable many-body systems is of vigorous interest. In such systems, the spectral form factor (SFF), defined as the Fourier transform of two-level spectral correlation function, is known to exhibit random matrix theory (RMT) behaviors, namely a 'ramp' followed by a 'plateau' in sufficiently late time. Recently, a generic early-time deviation from the RMT behavior, which we call the 'bump', has been shown to exist in random quantum circuits and spin chains as toy models for many-body quantum chaotic systems. Here we demonstrate the existence of the 'bump-ramp-plateau' behavior in the SFF for a number of paradigmatic, stroboscopically-driven cold atom models of interacting bosons in optical lattices and spinor condensates. We find that the scaling of the many-body Thouless time $t_{\text{Th}}$ -- the time of the onset of the (RMT) ramp behavior -- and the increase of the bump amplitude in atom number are significantly slower in (effectively 0D) chaotic spinor gases than in 1D optical lattices, demonstrating the role of locality in many-body quantum chaos. Moreover, $t_{\text{Th}}$ scaling and the bump amplitude are more sensitive to variations in atom number than the system size regardless of the hyperfine structure, the symmetry classes, or the choice of the driving protocol. We obtain scaling functions of SFF which suggest power-law behavior for the bump regime in quantum chaotic cold-atom systems. Finally, we propose an interference measurement protocol to probe SFF in the laboratory.Comment: 10 pages, 7 figures, supplementary materia

Complete Hilbert-Space Ergodicity in Quantum Dynamics of Generalized Fibonacci Drives

Ergodicity of quantum dynamics is often defined through statistical properties of energy eigenstates, as exemplified by Berry's conjecture in single-particle quantum chaos and the eigenstate thermalization hypothesis in many-body settings. In this work, we investigate whether quantum systems can exhibit a stronger form of ergodicity, wherein any time-evolved state uniformly visits the entire Hilbert space over time. We call such a phenomenon complete Hilbert-space ergodicity (CHSE), which is more akin to the intuitive notion of ergodicity as an inherently dynamical concept. CHSE cannot hold for time-independent or even time-periodic Hamiltonian dynamics, owing to the existence of (quasi)energy eigenstates which precludes exploration of the full Hilbert space. However, we find that there exists a family of aperiodic, yet deterministic drives with minimal symbolic complexity -- generated by the Fibonacci word and its generalizations -- for which CHSE can be proven to occur. Our results provide a basis for understanding thermalization in general time-dependent quantum systems.Comment: 6 pages, 3 figures (main text); 14 pages, 3 figures (supplemental material