The inefficiency of re-weighted sampling and the curse of system size in high order path integration

Computing averages over a target probability density by statistical re-weighting of a set of samples with a different distribution is a strategy which is commonly adopted in fields as diverse as atomistic simulation and finance. Here we present a very general analysis of the accuracy and efficiency of this approach, highlighting some of its weaknesses. We then give an example of how our results can be used, specifically to assess the feasibility of high-order path integral methods. We demonstrate that the most promising of these techniques -- which is based on re-weighted sampling -- is bound to fail as the size of the system is increased, because of the exponential growth of the statistical uncertainty in the re-weighted average

Giant pop-ins and amorphization in germanium during indentation

Sudden excursions of unusually large magnitude (>1 μm), “giant pop-ins,” have been observed in the force-displacement curve for high load indentation of crystalline germanium(Ge). A range of techniques including Raman microspectroscopy, focused ion-beam cross sectioning, and transmission electron microscopy, are applied to study this phenomenon. Amorphous material is observed in residual indents following the giant pop-in. The giant pop-in is shown to be a material removal event, triggered by the development of shallow lateral cracks adjacent to the indent. Enhanced depth recovery, or “elbowing,” observed in the force-displacement curve following the giant pop-in is explained in terms of a compliant response of plates of material around the indent detached by lateral cracking. The possible causes of amorphization are discussed, and the implications in light of earlier indentation studies of Ge are considered

Predicting the movements of permanently installed electrodes on an active landslide using time-lapse geoelectrical resistivity data only

If electrodes move during geoelectrical resistivity monitoring and their new positions are not incorporated in the inversion, then the resulting tomographic images exhibit artefacts that can obscure genuine time-lapse resistivity changes in the subsurface. The effects of electrode movements on time-lapse resistivity tomography are investigated using a simple analytical model and real data. The correspondence between the model and the data is sufficiently good to be able to predict the effects of electrode movements with reasonable accuracy. For the linear electrode arrays and 2D inversions under consideration, the data are much more sensitive to longitudinal than transverse or vertical movements. Consequently the model can be used to invert the longitudinal offsets of the electrodes from their known baseline positions using only the time-lapse ratios of the apparent resistivity data. The example datasets are taken from a permanently installed electrode array on an active lobe of a landslide. Using two sets with different levels of noise and subsurface resistivity changes, it is found that the electrode positions can be recovered to an accuracy of 4 % of the baseline electrode spacing. This is sufficient to correct the artefacts in the resistivity images, and provides for the possibility of monitoring the movement of the landslide and its internal hydraulic processes simultaneously using electrical resistivity tomography only

Detection of Composite Delaminations and Broken Solder Joints by a Full-Field Laser Doppler Technique

A method for full-field non-contact vibration measurement based on the Michelson Interferometer has been developed and applied to a wide range of components and structures. Unlike other optical techniques such as holography, the vibration imager does not require a specialized laboratory and stable environment, works over a much wider dynamic range,and the vibration time history is available for a more detailed analysis of the structures response. Use of this technique to detect delaminations in graphite/epoxy specimens is explored in this paper. The data was compared with X-ray and ultrasonic methods. The integrity of solder joints in electronic circuit boards has also been studied by this method at the University of Wisconsin, Madison and is also presented in this paper

Quantum Nature of Light Measured With a Single Detector

We realized the most fundamental quantum optical experiment to prove the non-classical character of light: Only a single quantum emitter and a single superconducting nanowire detector were used. A particular appeal of our experiment is its elegance and simplicity. Yet its results unambiguously enforce a quantum theory for light. Previous experiments relied on more complex setups, such as the Hanbury-Brown-Twiss configuration, where a beam splitter directs light to two photodetectors, giving the false impression that the beam splitter is required. Our work results in a major simplification of the widely used photon-correlation techniques with applications ranging from quantum information processing to single-molecule detection.Comment: 7 page

Hedgehog Signalling in Androgen Independent Prostate Cancer

Objectives: Androgen-deprivation therapy effectively shrinks hormone-naïve prostate cancer, both in the prostate and at sites of distant metastasis. However prolonged androgen deprivation generally results in relapse and androgen-independent tumour growth, which is inevitably fatal. The molecular events that enable prostate cancer cells to proliferate in reduced androgen conditions are poorly understood. Here we investigate the role of Hedgehog signalling in androgen-independent prostate cancer (AIPC). Methods: Activity of the Hedgehog signalling pathway was analysed in cultured prostate cancer cells, and circulating prostate tumour cells were isolated from blood samples of patients with AIPC. Results: AIPC cells were derived through prolonged culture in reduced androgen conditions, modelling hormone therapy in patients, and expressed increased levels of Hedgehog signalling proteins. Exposure of cultured AIPC cells to cyclopamine, which inhibits Hedgehog signalling, resulted in inhibition of cancer cell growth. The expression of the Hedgehog receptor PTCH and the highly prostate cancer-specific gene DD3PCA3 was significantly higher in circulating prostate cancer cells isolated from patients with AIPC compared with samples prepared from normal individuals. There was an association between PTCH and DD3PCA3 expression and the length of androgen-ablation therapy. Conclusions: Our data are consistent with reports implicating overactivity of Hedgehog signalling in prostate cancer and suggest that Hedgehog signalling contributes to the androgen-independent growth of prostate cancer cells. As systemic anti-Hedgehog medicines are developed, the Hedgehog pathway will become a potential new therapeutic target in advanced prostate cancer.Peer reviewedFinal Accepted Versio

A Comparative Analysis of the Relationship Between Employee Perceptions of an Organizational Leader\u27s Commitment to Safety and Actual Injury Rates in a University Setting

The purpose of this study was to explore the correlation between employee perceptions of their supervisor’s commitment to safety (safety climate) and the actual rate of occupational injuries among the same employees. The study also aimed to examine the relationship between the employee perceptions of their supervisor’s leadership practices and the supervisor’s safety climate rating. In addition, this study examined the potential influence of employee demographic factors on their responses to survey questions. This research study sought to answer three primary questions: (1) Does a significant correlation exist between employee perceptions of his supervisor’s commitment to the health and safety of workers and actual injury/illness rates within an organization? (2) Does a significant correlation exist between specific leadership practices of supervisors and their safety climate ratings as perceived by their employees? (3) Is there a significant difference in employee views on safety climate and leadership practices of their supervisor based on employee demographic variables including gender, education level, skilled versus non-skilled positions, time in position, or shift assignment? Previous studies of similar construct focused on industrial settings such as manufacturing, construction, and oil and gas exploration. This study focused on workers engaged in maintenance type functions within the non-industrial setting of a university. The construct and findings of this study has applicability in a variety of settings including healthcare, general business, etc. Developing an understanding of the role that supervisors play in actively driving safety programs that affect their subordinates provides valuable insight into elements of supervisor selection and training. A survey instrument was developed utilizing a combination of previously validated “safety climate” questions, along with selected general leadership questions. A 7- point Likert scale was employed for the safety climate and leadership practices questions. Demographic questions were included to provide critical data for application for research question three. In addition, three questions were included to solicit data regarding each respondent’s injury experience for the previous 12 month period. The findings of this study, while in several instances not yielding statistically significant data, support several key assertions that appear to have relevancy in the study and practice of the critical importance of leadership in providing a safe workplace. A strong correlation emerged between participant responses to safety climate and general leadership actions questions, demonstrating the interrelationship of leadership to safety. In addition, the findings indicated that demographic factors including gender, education level, length of service, and assigned work shift had negligible effect on employee views of their leaders. The results of this study provide useful information regarding the influence of supervisor’s actions upon the safety performance of their employees. In addition, the study helps validate the relationship of general leadership practices of supervisors to the overall safety climate of their work groups. While additional research into the concept and practical application of safety climate as a predictor of safety performance should be undertaken, the findings of this study add to collective knowledge of the subject