Query Complexity of Derivative-Free Optimization

This paper provides lower bounds on the convergence rate of Derivative Free Optimization (DFO) with noisy function evaluations, exposing a fundamental and unavoidable gap between the performance of algorithms with access to gradients and those with access to only function evaluations. However, there are situations in which DFO is unavoidable, and for such situations we propose a new DFO algorithm that is proved to be near optimal for the class of strongly convex objective functions. A distinctive feature of the algorithm is that it uses only Boolean-valued function comparisons, rather than function evaluations. This makes the algorithm useful in an even wider range of applications, such as optimization based on paired comparisons from human subjects, for example. We also show that regardless of whether DFO is based on noisy function evaluations or Boolean-valued function comparisons, the convergence rate is the same

Prevention of headache after lumbar puncture: questionnaire survey of neurologists and neurosurgeons in United Kingdom

No abstract available

Expression of natural killer receptor alleles at different Ly49 loci occurs independently and is regulated by major histocompatibility complex class I molecules.

Ly49 receptor genes are expressed by subsets of natural killer (NK) cells in an overlapping fashion, accounting for the capacity of NK subsets to attack host cells that have selectively downregulated self-major histocompatibility complex (MHC) class I molecules. It was shown previously that most NK cells express only one or the other allele of a given Ly49 gene, while a smaller population expresses both alleles. However, the methods used to detect monoallelic and biallelic cells were nonquantitative. Here, new allele-specific antibodies were used to provide the first quantitative examination of biallelic and monoallelic expression of Ly49A and Ly49G2. The results demonstrate conclusively that most Ly49A(+) and Ly49G2(+) NK cells express the corresponding gene in a monoallelic fashion, with a smaller subset expressing both alleles. Unexpectedly, biallelic Ly49A(+) NK cells were more numerous than predicted by completely independent allelic expression, suggesting some heterogeneity among NK progenitors in the potential to express a given Ly49 gene. The data also show that cells expressing one allele of Ly49G2 may express Ly49A from the same or opposite chromosome with equal likelihood, indicating that the expressed allele is chosen independently for different Ly49 genes. Finally, the data demonstrate that biallelic expression of Ly49A or Ly49G2 occurs least frequently in mice that express ligands for these receptors (H-2(d) mice), and most frequently in class I-deficient mice. Thus, biallelic expression of Ly49 genes is regulated by interactions of NK cell progenitors with MHC class I molecules

Analysis and Geometric Optimization of Single Electron Transistors for Read-Out in Solid-State Quantum Computing

The single electron transistor (SET) offers unparalled opportunities as a nano-scale electrometer, capable of measuring sub-electron charge variations. SETs have been proposed for read-out schema in solid-state quantum computing where quantum information processing outcomes depend on the location of a single electron on nearby quantum dots. In this paper we investigate various geometries of a SET in order to maximize the device's sensitivity to charge transfer between quantum dots. Through the use of finite element modeling we model the materials and geometries of an Al/Al2O3 SET measuring the state of quantum dots in the Si substrate beneath. The investigation is motivated by the quest to build a scalable quantum computer, though the methodology used is primarily that of circuit theory. As such we provide useful techniques for any electronic device operating at the classical/quantum interface.Comment: 13 pages, 17 figure

Caring for continence in stroke care settings: a qualitative study of patients’ and staff perspectives on the implementation of a new continence care intervention

Objectives: Investigate the perspectives of patients and nursing staff on the implementation of an augmented continence care intervention after stroke. Design: Qualitative data were elicited during semi-structured interviews with patients (n = 15) and staff (14 nurses; nine nursing assistants) and analysed using thematic analysis. Setting: Mixed acute and rehabilitation stroke ward. Participants: Stroke patients and nursing staff that experienced an enhanced continence care intervention. Results: Four themes emerged from patients’ interviews describing: (a) challenges communicating about continence (initiating conversations and information exchange); (b) mixed perceptions of continence care; (c) ambiguity of focus between mobility and continence issues; and (d) inconsistent involvement in continence care decision making. Patients’ perceptions reflected the severity of their urinary incontinence. Staff described changes in: (i) knowledge as a consequence of specialist training; (ii) continence interventions (including the development of nurse-led initiatives to reduce the incidence of unnecessary catheterisation among patients admitted to their ward); (iii) changes in attitude towards continence from containment approaches to continence rehabilitation; and (iv) the challenges of providing continence care within a stroke care context including limitations in access to continence care equipment or products, and institutional attitudes towards continence. Conclusion: Patients (particularly those with severe urinary incontinence) described challenges communicating about and involvement in continence care decisions. In contrast, nurses described improved continence knowledge, attitudes and confidence alongside a shift from containment to rehabilitative approaches. Contextual components including care from point of hospital admission, equipment accessibility and interdisciplinary approaches were perceived as important factors to enhancing continence care