High-power, low-phase-noise, frequency-agile laser system for delivering fiber-noise-canceled pulses for strontium clock atom interferometry.

We present a laser system for performing single-photon atom interferometry on the 698 nm clock transition in ultracold strontium. We coherently combine the power of two titanium:sapphire lasers and demonstrate chirps of 200 MHz in 2.5 ms while phase-locked to an optical reference. Moreover, we demonstrate a novel, to the best of our knowledge, scheme to deliver 4 W pulsed beams to the atoms via a mode-cleaning optical fiber using active noise cancellation.

The prevalence and risk factors of depression in engineering college students: A cross-sectional study.

Background: Engineering students like any other students face several stressors in their lives, which make them vulnerable to depression. Depression may affect students' academic performance. Aim: The present study aims to estimate the prevalence and associated risk factors of depression among engineering students. Material and Methods: A cross-sectional study was conducted in December 2016 among 110 randomly selected students from an engineering college in a rural area of Pune district, India. PHQ-9 questionnaire was used. Univariate and multivariable ordinal logistic regression was used to quantify association. Results: Of a total of 110 students, 71.8% were males, while 28.2% were females. The mean age was 20.7 years. 29.1% had no depression, 48.2% had mild depression, and 22.7% had moderate depression. Univariate analysis found four variables significantly associated with a greater risk of depression: parental stress, sibling stress, economic stress, and interpersonal conflict. In the adjusted (multivariable) ordinal logistic regression analysis controlling for all independent variables, only lack of economic support and interpersonal conflicts retained their statistical significance. Conclusion: The prevalence of depression in engineering students is high and strongly associated with the presence of economic and personal stress. Screening for depression and giving them care and support is of paramount importance.

Information decay and enzymatic information recovery for DNA data storage.

Synthetic DNA has been proposed as a storage medium for digital information due to its high theoretical storage density and anticipated long storage horizons. However, under all ambient storage conditions, DNA undergoes a slow chemical decay process resulting in nicked (broken) DNA strands, and the information stored in these strands is no longer readable. In this work we design an enzymatic repair procedure, which is applicable to the DNA pool prior to readout and can partially reverse the damage. Through a chemical understanding of the decay process, an overhang at the 3' end of the damaged site is identified as obstructive to repair via the base excision-repair (BER) mechanism. The obstruction can be removed via the enzyme apurinic/apyrimidinic endonuclease I (APE1), thereby enabling repair of hydrolytically damaged DNA via Bst polymerase and Taq ligase. Simulations of damage and repair reveal the benefit of the enzymatic repair step for DNA data storage, especially when data is stored in DNA at high storage densities (=low physical redundancy) and for long time durations.

Inversion symmetry and bulk Rashba effect in methylammonium lead iodide perovskite single crystals.

Methylammonium lead iodide perovskite (MAPbI3) exhibits long charge carrier lifetimes that are linked to its high efficiency in solar cells. Yet, the mechanisms governing these unusual carrier dynamics are not completely understood. A leading hypothesis-disproved in this work-is that a large, static bulk Rashba effect slows down carrier recombination. Here, using second harmonic generation rotational anisotropy measurements on MAPbI3 crystals, we demonstrate that the bulk structure of tetragonal MAPbI3 is centrosymmetric with I4/mcm space group. Our calculations show that a significant Rashba splitting in the bandstructure requires a non-centrosymmetric lead iodide framework, and that incorrect structural relaxations are responsible for the previously predicted large Rashba effect. The small Rashba splitting allows us to compute effective masses in excellent agreement with experiment. Our findings rule out the presence of a large static Rashba effect in bulk MAPbI3, and our measurements find no evidence of dynamic Rashba effects.