Nanosecond electro-optical switching with a repetition rate above 20MHz

We describe an electro-optical switch based on a commercial electro-optic modulator (modified for high-speed operation) and a 340V pulser having a rise time of 2.2ns (at 250V). It can produce arbitrary pulse patterns with an average repetition rate beyond 20MHz. It uses a grounded-grid triode driven by transmitting power transistors. We discuss variations that enable analog operation, use the step-recovery effect in bipolar transistors, or offer other combinations of output voltage, size, and cost.Comment: 3 pages, 3 figures. Minor change

Atom-wave diffraction between the Raman-Nath and the Bragg regime: Effective Rabi frequency, losses, and phase shifts

We present an analytic theory of the diffraction of (matter) waves by a lattice in the "quasi-Bragg" regime, by which we mean the transition region between the long-interaction Bragg and "channelling" regimes and the short-interaction Raman-Nath regime. The Schroedinger equation is solved by adiabatic expansion, using the conventional adiabatic approximation as a starting point, and re-inserting the result into the Schroedinger equation to yield a second order correction. Closed expressions for arbitrary pulse shapes and diffraction orders are obtained and the losses of the population to output states otherwise forbidden by the Bragg condition are derived. We consider the phase shift due to couplings of the desired output to these states that depends on the interaction strength and duration and show how these can be kept negligible by a choice of smooth (e.g., Gaussian) envelope functions even in situations that substantially violate the adiabaticity condition. We also give an efficient method for calculating the effective Rabi frequency (which is related to the eigenvalues of Mathieu functions) in the quasi-Bragg regime.Comment: Minor additions, more concise text. To appear in Phys. Rev. A. 20 pages, 10 figure

A Precision Angle Sensor using an Optical Lever inside a Sagnac Interferometer

We built an ultra low noise angle sensor by combining a folded optical lever and a Sagnac interferometer. The instrument has a measured noise floor of 1.3 prad / Hz^(1/2) at 2.4 kHz. We achieve this record angle sensitivity using a proof-of-concept apparatus with a conservative N=11 bounces in the optical lever. This technique could be extended to reach sub-picoradian / Hz^(1/2) sensitivities with an optimized design.Comment: 3 pages, 4 figure

Broadband Optical Serrodyne Frequency Shifting

We demonstrate serrodyne frequency shifting of light from 200 MHz to 1.2 GHz with an efficiency of better than 60 percent. The frequency shift is imparted by an electro-optic phase modulator driven by a high-frequency, high-fidelity sawtooth waveform that is passively generated by a commercially available Non-Linear Transmission Line (NLTL). We also implement a push-pull configuration using two serrodyne-driven phase modulators allowing for continuous tuning between -1.6 GHz and +1.6 GHz. Compared to competing technologies, this technique is simple and robust, and offers the largest available tuning range in this frequency band.Comment: 3 pages, 4 figure

A new photon recoil experiment: towards a determination of the fine structure constant

We report on progress towards a measurement of the fine structure constant to an accuracy of $5\times 10^{-10}$ or better by measuring the ratio of the Planck constant to the mass of the cesium atom. Compared to similar experiments, ours is improved in three significant ways: (i) simultaneous conjugate interferometers, (ii) multi-photon Bragg diffraction between same internal states, and (iii) an about 1000 fold reduction of laser phase noise to -138 dBc/Hz. Combining that with a new method to simultaneously stabilize the phases of four frequencies, we achieve 0.2 mrad effective phase noise at the location of the atoms. In addition, we use active stabilization to suppress systematic effects due to beam misalignment.Comment: 12 pages, 9 figure

Exploring the limits of ultracold atoms in space

Existing space-based cold atom experiments have demonstrated the utility of microgravity for improvements in observation times and for minimizing the expansion energy and rate of a freely evolving coherent matter wave. In this paper we explore the potential for space-based experiments to extend the limits of ultracold atoms utilizing not just microgravity, but also other aspects of the space environment such as exceptionally good vacuums and extremely cold temperatures. The tantalizing possibility that such experiments may one day be able to probe physics of quantum objects with masses approaching the Planck mass is discussed

Parental perceptions of childhood seasonal influenza vaccination in Singapore: A cross-sectional survey.

Seasonal influenza vaccination is recommended in children aged 6-59months, but little is known about child vaccination coverage and determinants in Asian settings. We report the results of a survey of knowledge, attitudes, practices, and determinants of child influenza vaccination in Singapore. In December 2015-March 2016, we conducted a survey of 332 parents of children aged 6months to 5years attending pre-schools. We assessed child influenza vaccine coverage and parental knowledge, attitudes, and practices of child influenza vaccination. We used multivariable regression and structural equation models to identify factors associated with child influenza vaccination. Knowledge about influenza, perceived benefit of vaccination, and willingness to vaccinate were high. However, only 32% of children had ever received influenza vaccine, and only 15% in the past year. Factors independently associated with child influenza vaccination included: being recommended influenza vaccine by a child's doctor (prevalence ratio (PR)=2.47, 95% CI: 1.75-3.48); receiving influenza vaccine information from a private general practitioner (PR=1.47, 95% CI: 1.05-2.04); regularly receiving pre-travel influenza vaccine (PR=1.64, 95% CI: 1.19-2.25); higher willingness to vaccinate (PR=1.58, 95% CI:1.24-2.04 per unit increase in willingness score); and feeling well-informed about influenza vaccine (PR=1.44, 95% CI: 1.04-1.99). Parents who obtained influenza vaccine information from television were less likely to have vaccinated their child (PR=0.44, 95% CI: 0.23-0.85). Path analysis indicated that being recommended vaccination by a child's doctor increased willingness to vaccinate and self-efficacy (feeling well-informed about influenza vaccine). Median willingness-to-pay for a dose of influenza vaccine was SGD30 (interquartile range: SGD20-SGD50), and was higher in parents of vaccinated compared with unvaccinated children (SGD45vs SGD30, p=0.0012). Knowledge and willingness to vaccinate was high in this parent population, but influenza vaccine uptake in children was low. Encouraging medical professionals to recommend vaccination of eligible children is key to improving uptake

Global overview of the management of acute cholecystitis during the COVID-19 pandemic (CHOLECOVID study)

Background: This study provides a global overview of the management of patients with acute cholecystitis during the initial phase of the COVID-19 pandemic. Methods: CHOLECOVID is an international, multicentre, observational comparative study of patients admitted to hospital with acute cholecystitis during the COVID-19 pandemic. Data on management were collected for a 2-month study interval coincident with the WHO declaration of the SARS-CoV-2 pandemic and compared with an equivalent pre-pandemic time interval. Mediation analysis examined the influence of SARS-COV-2 infection on 30-day mortality. Results: This study collected data on 9783 patients with acute cholecystitis admitted to 247 hospitals across the world. The pandemic was associated with reduced availability of surgical workforce and operating facilities globally, a significant shift to worse severity of disease, and increased use of conservative management. There was a reduction (both absolute and proportionate) in the number of patients undergoing cholecystectomy from 3095 patients (56.2 per cent) pre-pandemic to 1998 patients (46.2 per cent) during the pandemic but there was no difference in 30-day all-cause mortality after cholecystectomy comparing the pre-pandemic interval with the pandemic (13 patients (0.4 per cent) pre-pandemic to 13 patients (0.6 per cent) pandemic; P = 0.355). In mediation analysis, an admission with acute cholecystitis during the pandemic was associated with a non-significant increased risk of death (OR 1.29, 95 per cent c.i. 0.93 to 1.79, P = 0.121). Conclusion: CHOLECOVID provides a unique overview of the treatment of patients with cholecystitis across the globe during the first months of the SARS-CoV-2 pandemic. The study highlights the need for system resilience in retention of elective surgical activity. Cholecystectomy was associated with a low risk of mortality and deferral of treatment results in an increase in avoidable morbidity that represents the non-COVID cost of this pandemic