151 research outputs found
Magnetic Trapping of Cold Bromine Atoms
Magnetic trapping of bromine atoms at temperatures in the milliKelvin regime
is demonstrated for the first time. The atoms are produced by photodissociation
of Br molecules in a molecular beam. The lab-frame velocity of Br atoms is
controlled by the wavelength and polarization of the photodissociation laser.
Careful selection of the wavelength results in one of the pair of atoms having
sufficient velocity to exactly cancel that of the parent molecule, and it
remains stationary in the lab frame. A trap is formed at the null point between
two opposing neodymium permanent magnets. Dissociation of molecules at the
field minimum results in the slowest fraction of photofragments remaining
trapped. After the ballistic escape of the fastest atoms, the trapped slow
atoms are only lost by elastic collisions with the chamber background gas. The
measured loss rate is consistent with estimates of the total cross section for
only those collisions transferring sufficient kinetic energy to overcome the
trapping potential
Collisional trap losses of cold, magnetically-trapped Br atoms
Near-threshold photodissociation of Br from a supersonic beam produces
slow bromine atoms that are trapped in the magnetic field minimum formed
between two opposing permanent magnets. Here, we quantify the dominant trap
loss rate due to collisions with two sources of residual gas: the background
limited by the vacuum chamber base pressure, and the carrier gas during the
supersonic gas pulse. The loss rate due to collisions with residual Ar in the
background follows pseudo first-order kinetics, and the bimolecular rate
coefficient for collisional loss from the trap is determined by measurement of
this rate as a function of the background Ar pressure. This rate coefficient is
smaller than the total elastic collision rate coefficient, as it only samples
those collisions that lead to trap loss, and is determined to be
. The calculated differential cross section can be used with this
value to estimate a trap depth of . Carrier gas collisions
occur only during the tail of the supersonic beam pulse. Using the differential
cross section verified by the background-gas collision measurements provides an
estimate of the peak molecular beam density of
in good agreement with the
prediction of a simple supersonic expansion model. Finally, we estimate the
trap loss rate due to Majorana transitions to be negligible, owing to the
relatively large trapped-atom phase-space volume
Real-time super-resolved 3D in turbid water using a fast range-gated CMOS camera
We present a range-gated camera system designed for real-time (10 Hz) 3D estimation underwater. The system uses a fast-shutter CMOS sensor (1280×1024 1280×1024 ) customized to facilitate gating with 1.67 ns (18.8 cm in water) delay steps relative to the triggering of a solid-state actively Q -switched 532 nm laser. A depth estimation algorithm has been carefully designed to handle the effects of light scattering in water, i.e., forward and backward scattering. The raw range-gated signal is carefully filtered to reduce noise while preserving the signal even in the presence of unwanted backscatter. The resulting signal is proportional to the number of photons that are reflected during a small time unit (range), and objects will show up as peaks in the filtered signal. We present a peak-finding algorithm that is robust to unwanted forward scatter peaks and at the same time can pick out distant peaks that are barely higher than peaks caused by sensor and intensity noise. Super-resolution is achieved by fitting a parabola around the peak, which we show can provide depth precision below 1 cm at high signal levels. We show depth estimation results when scanning a range of 8 m (typically 1–9 m) at 10 Hz. The results are dependent on the water quality. We are capable of estimating depth at distances of over 4.5 attenuation lengths when imaging high albedo targets at low attenuation lengths, and we achieve a depth resolution () (σ)ranging from 0.8 to 9 cm, depending on signal level.publishedVersio
Detecting RNA base methylations in single cells by in situ hybridization.
Methylated bases in tRNA, rRNA and mRNA control a variety of cellular processes, including protein synthesis, antimicrobial resistance and gene expression. Currently, bulk methods that report the average methylation state of ~104-107 cells are used to detect these modifications, obscuring potentially important biological information. Here, we use in situ hybridization of Molecular Beacons for single-cell detection of three methylations (m62A, m1G and m3U) that destabilize Watson-Crick base pairs. Our method-methylation-sensitive RNA fluorescence in situ hybridization-detects single methylations of rRNA, quantifies antibiotic-resistant bacteria in mixtures of cells and simultaneously detects multiple methylations using multicolor fluorescence imaging
Pyrethroids and Nectar Toxins Have Subtle Effects on the Motor Function, Grooming and Wing Fanning Behaviour of Honeybees (Apis mellifera)
Sodium channels, found ubiquitously in animal muscle cells and neurons, are one of the main target sites of many naturally-occurring, insecticidal plant compounds and agricultural pesticides. Pyrethroids, derived from compounds found only in the Asteraceae, are particularly toxic to insects and have been successfully used as pesticides including on flowering crops that are visited by pollinators. Pyrethrins, from which they were derived, occur naturally in the nectar of some flowering plant species. We know relatively little about how such compounds—i.e., compounds that target sodium channels—influence pollinators at low or sub-lethal doses. Here, we exposed individual adult forager honeybees to several compounds that bind to sodium channels to identify whether these compounds affect motor function. Using an assay previously developed to identify the effect of drugs and toxins on individual bees, we investigated how acute exposure to 10 ng doses (1 ppm) of the pyrethroid insecticides (cyfluthrin, tau-fluvalinate, allethrin and permethrin) and the nectar toxins (aconitine and grayanotoxin I) affected honeybee locomotion, grooming and wing fanning behaviour. Bees exposed to these compounds spent more time upside down and fanning their wings. They also had longer bouts of standing still. Bees exposed to the nectar toxin, aconitine, and the pyrethroid, allethrin, also spent less time grooming their antennae. We also found that the concentration of the nectar toxin, grayanotoxin I (GTX), fed to bees affected the time spent upside down (i.e., failure to perform the righting reflex). Our data show that low doses of pyrethroids and other nectar toxins that target sodium channels mainly influence motor function through their effect on the righting reflex of adult worker honeybees
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