Rapid mapping of visual receptive fields by filtered back-projection: application to multi-neuronal electrophysiology and imaging

Neurons in the visual system vary widely in the spatiotemporal properties of their receptive fields (RFs), and understanding these variations is key to elucidating how visual information is processed. We present a new approach for mapping RFs based on the filtered back projection (FBP), an algorithm used for tomographic reconstructions. To estimate RFs, a series of bars were flashed across the retina at pseudo‐random positions and at a minimum of five orientations. We apply this method to retinal neurons and show that it can accurately recover the spatial RF and impulse response of ganglion cells recorded on a multi‐electrode array. We also demonstrate its utility for in vivo imaging by mapping the RFs of an array of bipolar cell synapses expressing a genetically encoded Ca2+ indicator. We find that FBP offers several advantages over the commonly used spike‐triggered average (STA): (i) ON and OFF components of a RF can be separated; (ii) the impulse response can be reconstructed at sample rates of 125 Hz, rather than the refresh rate of a monitor; (iii) FBP reveals the response properties of neurons that are not evident using STA, including those that display orientation selectivity, or fire at low mean spike rates; and (iv) the FBP method is fast, allowing the RFs of all the bipolar cell synaptic terminals in a field of view to be reconstructed in under 4 min. Use of the FBP will benefit investigations of the visual system that employ electrophysiology or optical reporters to measure activity across populations of neurons

Hybrid III-V diamond photonic platform for quantum nodes based on neutral silicon vacancy centers in diamond

Integrating atomic quantum memories based on color centers in diamond with on-chip photonic devices would enable entanglement distribution over long distances. However, efforts towards integration have been challenging because color centers can be highly sensitive to their environment, and their properties degrade in nanofabricated structures. Here, we describe a heterogeneously integrated, on-chip, III-V diamond platform designed for neutral silicon vacancy (SiV0) centers in diamond that circumvents the need for etching the diamond substrate. Through evanescent coupling to SiV0 centers near the surface of diamond, the platform will enable Purcell enhancement of SiV0 emission and efficient frequency conversion to the telecommunication C-band. The proposed structures can be realized with readily available fabrication techniques

Improved simulated annealing based risk interaction network model for project risk response decisions

Risk interaction changes the probability and impact of a given risk, which may result in a less effective risk response decision (RD). This study presents an approach for supporting the project manager in making RDs, comprising a simulation model of risk interaction network (RIN) for evaluating the RDs and an improved simulated annealing (SA) algorithm for optimizing the RDs. The simulation model considers different risk levels and the corresponding risk interaction cases, which is closer to the reality. In addition to tailoring the SA algorithm to optimize RDs, it is improved through enhancing its neighborhood search with the aid of social network analysis. Specifically, two new network indices are designed for calculating the quantitative significance of RIN elements, i.e. the nodes that denote risks and edges that reflect the risk interactions. The element with a higher significance is more likely to be dealt with when generating a new RD in the neighborhood search. An application is provided to illustrate the utility of the proposed approach; a contrastive analysis of the improved SA and standard SA is also conducted to validate the effectiveness and efficiency of the former.A*STAR of Singapore (R-385-000-049-305), National Natural Science Foundation of China (71572094), Natural Science Foundation of Shandong Province (ZR2015GM015), and National Research Foundation of South Africa.https://www.elsevier.com/locate/dss2020-07-01hj2019Graduate School of Technology Management (GSTM

Socioeconomic Position and the Health Gradient in Cuba: Dimensions and Mechanisms

Background: To throw light on the under-researched association between socioeconomic position (SEP) and health in Cuba, this study examined SEP gradients in health and their underlying mechanisms among urban Cuban adults aged 18-65. Methods: By applying linear regressions to data from the 2010 National Survey on Risk Factors and Chronic Diseases, the analysis explored the SEP-health gradient along three SEP dimensions-education, occupation, and skin colour-using ten health measures: Self-reported health (SRH), general and abdominal obesity, hypertension, high glucose, high cholesterol, high triglycerides, low high-density lipoprotein cholesterol, metabolic syndrome, and cumulative risk factors. Regressions also included behaviours and health-related risk perceptions (tobacco and alcohol consumption, diet, physical activity, and risk-related behaviours). It thus investigated the SEP-health gradient and its underlying mechanisms via both behaviours and health-related risk perceptions. Results: Once controlling for gender, age, marital status, region and provincial dummies, the analysis detected educational gradients in SRH (estimated coefficient [95% CI]: Middle-level education = 3.535 [1.329, 5.741], p \u3c 0.01; high-level education = 5.249 [3.050, 7.448], p \u3c 0.01) that are partially explainable by both health-affecting behaviours (tobacco and alcohol consumption, diet, physical and sedentary activity) and risk perceptions. Using objective measures of health, however, it found no SEP-health gradients other than hypertension among people identified as having Black skin color (adjusted for demographic variables, 0.060 [0.018, 0.101], p \u3c 0.01) and high cholesterol among those identified as having Mulatto or Mestizo skin color (adjusted for demographic variables,-0.066 [-0.098,-0.033], p \u3c 0.01). Conclusions: In terms of objective health measures, the study provides minimal evidence for an SEP-health gradient in Cuba, results primarily attributable to the country\u27s universal healthcare system-which offers full coverage and access and affordable medications- A nd its highly developed education system

Hybrid Integration of GaP Photonic Crystal Cavities with Silicon-Vacancy Centers in Diamond by Stamp-Transfer

Optically addressable solid-state defects are emerging as one of the most promising qubit platforms for quantum networks. Maximizing photon-defect interaction by nanophotonic cavity coupling is key to network efficiency. We demonstrate fabrication of gallium phosphide 1-D photonic crystal waveguide cavities on a silicon oxide carrier and subsequent integration with implanted silicon-vacancy (SiV) centers in diamond using a stamp-transfer technique. The stamping process avoids diamond etching and allows fine-tuning of the cavities prior to integration. After transfer to diamond, we measure cavity quality factors ($Q$) of up to 8900 and perform resonant excitation of single SiV centers coupled to these cavities. For a cavity with $Q$ of 4100, we observe a three-fold lifetime reduction on-resonance, corresponding to a maximum potential cooperativity of $C = 2$. These results indicate promise for high photon-defect interaction in a platform which avoids fabrication of the quantum defect host crystal

A dosimetric analysis of the aeroformTM tissue expander in radiation therapy

Purpose: The aim of this study is to evaluate the effects of the metallic reservoir and the use of gas within the Aeroform™ tissue expander with respect to the radiation dose distribution.Methods: Dosimetric effects of using a metallic reservoir within a breast tissue expander during external beam radiotherapy were investigated. To view the internal components of the reservoir, it was removed from the tissue expander and imaged on a Varian AS500 electronic portal imager. To calculate the relative density of each component within the reservoir, an ionization chamber within solid water was used to measure the dose and compared to a simulation within the Pinnacle treatment planning system (TPS). To examine the relative dose profile along the length of the reservoir, the reservoir was exposed on EBT3 film and analyzed using SNC Patient™. In-vivo Dosimetry was performed using a RANDO® Woman phantom. Thermo-luminescent dosimeters were placed within the wax bolus enveloping the tissue expander.Results: Imaging the reservoir on the electronic portal imager revealed it consists of 3 distinct components. The densities assigned in the TPS, which resulted in calculated doses which matched the measured doses were; Section 1 = 0 g/cm3, Section 2 = 2.8 g/cm3 and Section 3 = 0.7 g/cm3. Relative dose reductions were observed due to the metallic case; Section 1 = 20%, Section 2 = 40% and Section 3 = 30%. Entrance doses ranged from 2.39 - 2.53 Gy for both the medial and lateral beams. Exit doses ranging from 1.10 - 1.71 Gy were observed in both beams. There was a significant difference in measured and calculated doses at exit locations in the beam.Conclusion: Dosimetric effects due to the metallic reservoir within the Aeroform breast tissue expander have been demonstrated and have been observed to be significant. To increase the dosimetric accuracy when contouring, individual components of the reservoir should be distinguished. Our in-vivo experiment showed that dose homogeneity was difficult due to the metallic reservoir and we recommend stringent patient dose monitoring when using this expander during radiotherapy.-----------------------------Cite this article as: Tran T, Ding W, Subramanian B, Melven L, Chao M, Farrow H, Baker C. A dosimetric analysis of the aeroformTM tissue expander in radiation therapy. Int J Cancer Ther Oncol 2014; 2(3):020316. DOI: 10.14319/ijcto.0203.1

Horava-Lifshitz Dark Energy

We formulate Horava-Lifshitz cosmology with an additional scalar field that leads to an effective dark energy sector. We find that, due to the inherited features from the gravitational background, Horava-Lifshitz dark energy naturally presents very interesting behaviors, possessing a varying equation-of-state parameter, exhibiting phantom behavior and allowing for a realization of the phantom divide crossing. In addition, Horava-Lifshitz dark energy guarantees for a bounce at small scale factors and it may trigger the turnaround at large scale factors, leading naturally to cyclic cosmology.Comment: 17 pages, no figures, version published at EJP

Characterizing and optimizing qubit coherence based on SQUID geometry

The dominant source of decoherence in contemporary frequency-tunable superconducting qubits is 1/$f$ flux noise. To understand its origin and find ways to minimize its impact, we systematically study flux noise amplitudes in more than 50 flux qubits with varied SQUID geometry parameters and compare our results to a microscopic model of magnetic spin defects located at the interfaces surrounding the SQUID loops. Our data are in agreement with an extension of the previously proposed model, based on numerical simulations of the current distribution in the investigated SQUIDs. Our results and detailed model provide a guide for minimizing the flux noise susceptibility in future circuits.Comment: 14 pages, 6 figure

Sliding wear of medium-carbon bainitic/martensitic/austenitic steel treated by short-term low-temperature austempering

A medium-carbon Si–Mn–Ni–Cr–Mo alloyed (300M) steel was austempered for various short periods at its martensite-starting temperature of 285 °C to seek improved sliding wear resistance as compared to the traditional martensitic and bainitic steels. Reciprocating sliding wear tests were performed against a WC/Co ball counterpart at a constant load of 49 N. The samples were characterised using field emission SEM, XRD and hardness testing. The associated wear mechanisms were analysed using SEM and cross-sectional TEM. The results revealed that a short austempering time of 6 min produced refined arrays of initial nano-bainitic ferrite laths and inter-lath filmy austenite and the majority martensite and retained austenite, while the majority of the microstructure remained martensitic with retained austenite. The hardness was unchanged to that of the as-quenched martensite of 6.4 GPa. Simultaneously the wear coefficient decreased by 41% from 2.67 to 1.58 × 10-15 m3N-1m-1, which is also superior to both the tempered martensite at 1.65 × 10-15 m3N-1m-1 and the lower bainite at 1.87 × 10-15 m3N-1m-1. Increasing the austempering time to 20 and 60 min resulted in wear coefficients of 1.38 and 2.18 × 10-15 m3N-1m-1, respectively. The improved wear resistance has been explained by the wear induced microstructure evolution, especially the carbon partitioning induced stabilisation of retained austenite. The high-stress sliding wear was found to be dominated by severe shear deformation, which resulted in a nano-laminate structured top layer. Delamination wear was found to take place within the embrittled nano-laminates