Self-calibrated Fourier transform spectrometer for laser-induced fluorescence spectroscopy with single-photon avalanche diode detection.

Fourier transform spectrometers are commonly used in scientific and industrial settings because of their ability to record complete spectra with high signal-to-noise ratios. Using a single-photon avalanche diode as the detector improves the sensitivity but adds complications in laser-induced fluorescence applications related to detector saturation and acquisition time exceeding the typical scan time. Here, we report a spectrometer for the detection of laser-induced fluorescence signal together with the excitation light, and use the second harmonic signal from the excitation light to correct the phase and calibrate the spectrum, removing the need for a separate calibration source. We achieve a resolution of 0.4cm-1 in the wavelength range of 1140.2 nm, and demonstrate detection of signals with powers as low as 377fW, with a noise floor of 172fW/cm-1.

Vignettes Identify Variation in Antibiotic Use for Suspected Early Onset Sepsis.

BACKGROUND AND OBJECTIVES: There is widespread unwarranted antibiotic use and large individual provider variation in antibiotic use in NICUs. Vignette-based research methodology offers a unique method of studying variation in individual provider decisions. The objective with this study was to use a vignette-based survey to identify specific areas of provider antibiotic use variation in newborns being evaluated for early onset sepsis. METHODS: This study was undertaken as part of a statewide multicenter neonatal antibiotic stewardship quality improvement project led by a perinatal quality improvement collaborative. A web-based vignette survey was administered to identify variation in decisions to start and discontinue antibiotics in cases of early onset sepsis. RESULTS: The largest variation was noted in 3 of the 6 vignette cases. These cases highlighted variation in (1) decisions to start antibiotics in a case describing a well-appearing newborn with risk factors and an elevated C-reactive protein, (2) decisions to start antibiotics in the case of a newborn with risk factors plus mild respiratory signs at birth, and (3) decisions to stop antibiotics in the case of the newborn with a history of sepsis risk factors and mild clinical respiratory signs that resolved after 72 hours. CONCLUSIONS: Clinical vignette assessment identified specific areas of variation in individual provider antibiotic use decisions in cases of suspected early onset sepsis. Vignettes are a valuable method of describing individual provider variation and highlighting antibiotic stewardship improvement opportunities in NICUs.

Spin Susceptibility above the Superfluid Onset in Ultracold Fermi Gases.

Ultracold atomic Fermi gases can be tuned to interact strongly, which produces a display of spectroscopic signatures above the superfluid transition reminiscent of the pseudogap in cuprates. However, the extent of the analogy can be questioned since many thermodynamic quantities in the low temperature spin-imbalanced normal state can be described successfully using Fermi liquid theory. Here we present spin susceptibility measurements across the interaction strength-temperature phase diagram using a novel radio frequency technique with ultracold ^{6}Li gases. For all significant interaction strengths and at all temperatures we find the spin susceptibility is reduced compared to the equivalent value for a noninteracting Fermi gas. At unitarity, we can use the local density approximation to extract the integrated spin susceptibility for the uniform gas as a function of temperature, which at high temperatures is generally less than theoretically predicted. At low temperatures, our data lie within the range of theoretical predictions, although we can also describe the entire curve using a very simple one-parameter mean field model with monotonically increasing spin susceptibility.

Prednisolone Versus Dexamethasone for Croup: a Randomized Controlled Trial.

OBJECTIVES: The use of either prednisolone or low-dose dexamethasone in the treatment of childhood croup lacks a rigorous evidence base despite widespread use. In this study, we compare dexamethasone at 0.6 mg/kg with both low-dose dexamethasone at 0.15 mg/kg and prednisolone at 1 mg/kg. METHODS: Prospective, double-blind, noninferiority randomized controlled trial based in 1 tertiary pediatric emergency department and 1 urban district emergency department in Perth, Western Australia. Inclusions were age >6 months, maximum weight 20 kg, contactable by telephone, and English-speaking caregivers. Exclusion criteria were known prednisolone or dexamethasone allergy, immunosuppressive disease or treatment, steroid therapy or enrollment in the study within the previous 14 days, and a high clinical suspicion of an alternative diagnosis. A total of 1252 participants were enrolled and randomly assigned to receive dexamethasone (0.6 mg/kg; n = 410), low-dose dexamethasone (0.15 mg/kg; n = 410), or prednisolone (1 mg/kg; n = 411). Primary outcome measures included Westley Croup Score 1-hour after treatment and unscheduled medical re-attendance during the 7 days after treatment. RESULTS: Mean Westley Croup Score at baseline was 1.4 for dexamethasone, 1.5 for low-dose dexamethasone, and 1.5 for prednisolone. Adjusted difference in scores at 1 hour, compared with dexamethasone, was 0.03 (95% confidence interval -0.09 to 0.15) for low-dose dexamethasone and 0.05 (95% confidence interval -0.07 to 0.17) for prednisolone. Re-attendance rates were 17.8% for dexamethasone, 19.5% for low-dose dexamethasone, and 21.7% for prednisolone (not significant [P = .59 and .19]). CONCLUSIONS: Noninferiority was demonstrated for both low-dose dexamethasone and prednisolone. The type of oral steroid seems to have no clinically significant impact on efficacy, both acutely and during the week after treatment.

Roton-maxon excitation spectrum of Bose condensates in a shaken optical lattice.

We present experimental evidence showing that an interacting Bose condensate in a shaken optical lattice develops a roton-maxon excitation spectrum, a feature normally associated with superfluid helium. The roton-maxon feature originates from the double-well dispersion in the shaken lattice, and can be controlled by both the atomic interaction and the lattice modulation amplitude. We determine the excitation spectrum using Bragg spectroscopy and measure the critical velocity by dragging a weak speckle potential through the condensate-both techniques are based on a digital micromirror device. Our dispersion measurements are in good agreement with a modified Bogoliubov model.

Mobile magnetic impurities in a Fermi superfluid: a route to designer molecules.

A magnetic impurity in a fermionic superfluid hosts bound quasiparticle states known as Yu-Shiba-Rusinov states. We argue here that, if the impurity is mobile (i.e., has a finite mass), the impurity and its bound Yu-Shiba-Rusinov quasiparticle move together as a midgap molecule, which has an unusual "Mexican-hat" dispersion that is tunable via the fermion density. We map out the impurity dispersion, which consists of an "atomic" branch (in which the impurity is dressed by quasiparticle pairs) and a "molecular" branch (in which the impurity binds a quasiparticle). We discuss the experimental realization and detection of midgap Shiba molecules, focusing on Li-Cs mixtures, and comment on the prospects they offer for realizing exotic many-body states.

Geometric scaling of Efimov states in a 6Li-¹³³Cs mixture.

In few-body physics, Efimov states are an infinite series of three-body bound states that obey universal discrete scaling symmetry when pairwise interactions are resonantly enhanced. Despite abundant reports of Efimov states in recent cold atom experiments, direct observation of the discrete scaling symmetry remains an elusive goal. Here we report the observation of three consecutive Efimov resonances in a heteronuclear Li-Cs mixture near a broad interspecies Feshbach resonance. The positions of the resonances closely follow a geometric series 1, λ, λ². The observed scaling constant λ(exp)=4.9(4) is in good agreement with the predicted value of 4.88.

Efficient continuous-duty Bitter-type electromagnets for cold atom experiments.

We present the design, construction, and characterization of Bitter-type electromagnets which can generate high magnetic fields under continuous operation with efficient heat removal for cold atom experiments. The electromagnets are constructed from a stack of alternating layers consisting of copper arcs and insulating polyester spacers. Efficient cooling of the copper is achieved via parallel rectangular water cooling channels between copper layers with low resistance to flow; a high ratio of the water-cooled surface area to the volume of copper ensures a short length scale (~1 mm) to extract dissipated heat. High copper fraction per layer ensures high magnetic field generated per unit energy dissipated. The ensemble is highly scalable and compressed to create a watertight seal without epoxy. From our measurements, a peak field of 770 G is generated 14 mm away from a single electromagnet with a current of 400 A and a total power dissipation of 1.6 kW. With cooling water flowing at 3.8 l/min, the coil temperature only increases by 7 °C under continuous operation.

Fluctuating stripes at the onset of the pseudogap in the high-T(c) superconductor Bi(2)Sr(2)CaCu(2)O(8+x).

Doped Mott insulators have a strong propensity to form patterns of holes and spins often referred to as stripes. In copper oxides, doping also gives rise to the pseudogap state, which can be transformed into a high-temperature superconducting state with sufficient doping or by reducing the temperature. A long-standing issue has been the interplay between the pseudogap, which is generic to all hole-doped copper oxide superconductors, and stripes, whose static form occurs in only one family of copper oxides over a narrow range of the phase diagram. Here we report observations of the spatial reorganization of electronic states with the onset of the pseudogap state in the high-temperature superconductor Bi(2)Sr(2)CaCu(2)O(8+x), using spectroscopic mapping with a scanning tunnelling microscope. We find that the onset of the pseudogap phase coincides with the appearance of electronic patterns that have the predicted characteristics of fluctuating stripes. As expected, the stripe patterns are strongest when the hole concentration in the CuO(2) planes is close to 1/8 (per copper atom). Although they demonstrate that the fluctuating stripes emerge with the onset of the pseudogap state and occur over a large part of the phase diagram, our experiments indicate that the stripes are a consequence of pseudogap behaviour rather than its cause.

Visualizing the formation of the Kondo lattice and the hidden order in URu(2)Si(2).

Heavy electronic states originating from the f atomic orbitals underlie a rich variety of quantum phases of matter. We use atomic scale imaging and spectroscopy with the scanning tunneling microscope to examine the novel electronic states that emerge from the uranium f states in URu(2)Si(2). We find that, as the temperature is lowered, partial screening of the f electrons' spins gives rise to a spatially modulated Kondo-Fano resonance that is maximal between the surface U atoms. At T = 17.5 K, URu(2)Si(2) is known to undergo a second-order phase transition from the Kondo lattice state into a phase with a hidden order parameter. From tunneling spectroscopy, we identify a spatially modulated, bias-asymmetric energy gap with a mean-field temperature dependence that develops in the hidden order state. Spectroscopic imaging further reveals a spatial correlation between the hidden order gap and the Kondo resonance, suggesting that the two phenomena involve the same electronic states.

Nanoscale proximity effect in the high-temperature superconductor Bi{2}Sr{2}CaCu{2}O{8+delta} using a scanning tunneling microscope.

High-temperature cuprate superconductors exhibit extremely local nanoscale phenomena and strong sensitivity to doping. While other experiments have looked at nanoscale interfaces between layers of different dopings, we focus on the interplay between naturally inhomogeneous nanoscale regions. Using scanning tunneling microscopy to carefully track the same region of the sample as a function of temperature, we show that regions with weak superconductivity can persist to elevated temperatures if bordered by regions of strong superconductivity. This suggests that it may be possible to increase the maximum possible transition temperature by controlling the distribution of dopants.

A regional initiative to reduce skin infections amongst aboriginal children living in remote communities of the Northern Territory, Australia.

BACKGROUND: Linked to extreme rates of chronic heart and kidney disease, pyoderma is endemic amongst Aboriginal children in Australia's Northern Territory (NT). Many of those with pyoderma will also have scabies. We report the results of a community-based collaboration within the East Arnhem Region, which aimed to reduce the prevalence of both skin infections in Aboriginal children. METHODOLOGY/PRINCIPAL FINDINGS: Commencing September 2004, we conducted an ecological study that included active surveillance for skin infections amongst children aged <15 years in five remote East Arnhem communities over a three year period. Screening was undertaken by trained local community workers, usually accompanied by another project team member, using a standard data collection form. Skin infections were diagnosed clinically with the aid of a pictorial flip chart developed for the purpose. Topical 5% permethrin was provided for age-eligible children and all household contacts whenever scabies was diagnosed, whilst those with pyoderma were referred to the clinic for treatment in accordance with current guidelines. In addition, annual mass scabies treatment (5% permethrin cream) was offered to all community residents in accordance with current guidelines but was not directly observed. Pyoderma and scabies prevalence per month was determined from 6038 skin assessments conducted on 2329 children. Pyoderma prevalence dropped from 46.7% at baseline to a median of 32.4% (IQR 28.9%-41.0%) during the follow-up period - an absolute reduction of 14.7% (IQR 4.7%-16.8%). Compared to the first 18 months of observation, there was an absolute reduction in pyoderma prevalence of 18 cases per 100 children (95%CI -21.0, -16.1, p

Topological surface states protected from backscattering by chiral spin texture.

Topological insulators are a new class of insulators in which a bulk gap for electronic excitations is generated because of the strong spin-orbit coupling inherent to these systems. These materials are distinguished from ordinary insulators by the presence of gapless metallic surface states, resembling chiral edge modes in quantum Hall systems, but with unconventional spin textures. A key predicted feature of such spin-textured boundary states is their insensitivity to spin-independent scattering, which is thought to protect them from backscattering and localization. Recently, experimental and theoretical efforts have provided strong evidence for the existence of both two- and three-dimensional classes of such topological insulator materials in semiconductor quantum well structures and several bismuth-based compounds, but so far experiments have not probed the sensitivity of these chiral states to scattering. Here we use scanning tunnelling spectroscopy and angle-resolved photoemission spectroscopy to visualize the gapless surface states in the three-dimensional topological insulator Bi(1-x)Sb(x), and examine in detail the influence of scattering from disorder caused by random alloying in this compound. We show that, despite strong atomic scale disorder, backscattering between states of opposite momentum and opposite spin is absent. Our observations demonstrate that the chiral nature of these states protects the spin of the carriers. These chiral states are therefore potentially useful for spin-based electronics, in which long spin coherence is critical, and also for quantum computing applications, where topological protection can enable fault-tolerant information processing.

Extending universal nodal excitations optimizes superconductivity in Bi2Sr2CaCu2O8+delta.

Understanding the mechanism by which d wave superconductivity in the cuprates emerges and is optimized by doping the Mott insulator is one of the major outstanding problems in condensed-matter physics. Our high-resolution scanning tunneling microscopy measurements of the high-transition temperature (Tc) superconductor Bi2Sr2CaCu2O8+delta show that samples with different Tc values in the low doping regime follow a remarkably universal d wave low-energy excitation spectrum, indicating a doping-independent nodal gap. We demonstrate that Tc instead correlates with the fraction of the Fermi surface over which the samples exhibit the universal spectrum. Optimal Tc is achieved when all parts of the Fermi surface follow this universal behavior. Increasing the temperature above Tc turns the universal spectrum into an arc of gapless excitations, whereas overdoping breaks down the universal nodal behavior.

Electronic origin of the inhomogeneous pairing interaction in the high-Tc superconductor Bi2Sr2CaCu2O8+delta.

Identifying the mechanism of superconductivity in the high-temperature cuprate superconductors is one of the major outstanding problems in physics. We report local measurements of the onset of superconducting pairing in the high-transition temperature (Tc) superconductor Bi2Sr2CaCu2O8+delta using a lattice-tracking spectroscopy technique with a scanning tunneling microscope. We can determine the temperature dependence of the pairing energy gaps, the electronic excitations in the absence of pairing, and the effect of the local coupling of electrons to bosonic excitations. Our measurements reveal that the strength of pairing is determined by the unusual electronic excitations of the normal state, suggesting that strong electron-electron interactions rather than low-energy (<0.1 volts) electron-boson interactions are responsible for superconductivity in the cuprates.