610 research outputs found
Double-lambda microscopic model for entangled light generation by four-wave-mixing
Motivated by recent experiments, we study four-wave-mixing in an atomic
double-{\Lambda} system driven by a far-detuned pump. Using the
Heisenberg-Langevin formalism, and based on the microscopic properties of the
medium, we calculate the classical and quantum properties of seed and conju-
gate beams beyond the linear amplifier approximation. A continuous variable
approach gives us access to relative-intensity noise spectra that can be
directly compared to experiments. Restricting ourselves to the cold-atom
regime, we predict the generation of quantum-correlated beams with a
relative-intensity noise spectrum well below the standard quantum limit (down
to -6 dB). Moreover entanglement between seed and conjugate beams measured by
an inseparability down to 0.25 is expected. This work opens the way to the
generation of entangled beams by four-wave mixing in a cold atomic sample.Comment: 11 pages, 6 figures, submitted to PR
Gradient echo memory in an ultra-high optical depth cold atomic ensemble
Quantum memories are an integral component of quantum repeaters - devices
that will allow the extension of quantum key distribution to communication
ranges beyond that permissible by passive transmission. A quantum memory for
this application needs to be highly efficient and have coherence times
approaching a millisecond. Here we report on work towards this goal, with the
development of a Rb magneto-optical trap with a peak optical depth of
1000 for the D2 transition using spatial and temporal
dark spots. With this purpose-built cold atomic ensemble to implement the
gradient echo memory (GEM) scheme. Our data shows a memory efficiency of % and coherence times up to 195 s, which is a factor of four greater
than previous GEM experiments implemented in warm vapour cells.Comment: 15 pages, 5 figure
Metal artefact reduction sequences for a piezoelectric bone conduction implant using a realistic head phantom in MRI
Industry standards require medical device manufacturers to perform
implant-induced artefact testing in phantoms at a pre-clinical stage to define
the extent of artefacts that can be expected during MRI. Once a device is
commercially available, studies on volunteers, cadavers or patients are
performed to investigate implant-induced artefacts and artefact reduction
methods more in-depth. This study describes the design and evaluation of a
realistic head phantom for pre-clinical implant-induced artefact testing in a
relevant environment. A case study is performed where a state-of-the-art
piezoelectric bone conduction implant is used in the 1.5 T and 3 T MRI
environments. Images were acquired using clinical and novel metal artefact
reducing (MARS) sequences at both field strengths. Artefact width and length
were measured in a healthy volunteer and compared with artefact sizes obtained
in the phantom. Artefact sizes are reported that are similar in shape between
the phantom and a volunteer, yet with dimensions differing up to 20% between
both. When the implant magnet is removed, the artefact size can be reduced
below a diameter of 5 cm, whilst the presence of an implant magnet and splint
creates higher artefacts up to 20 cm in diameter. Pulse sequences have been
altered to reduce the scan time up to 7 minutes, while preserving the image
quality. These results show that the anthropomorphic phantom can be used at a
preclinical stage to provide clinically relevant images, illustrating the
impact of the artefact on important brain structures.Comment: 17 pages, 5 figure
Spectroscopic measurement of the excitation spectrum on effectively curved spacetimes in a polaritonic fluid of light
Quantum fields in regions of extreme spacetime curvature give rise to a
wealth of effects, like Hawking radiation at the horizon of black holes. While
quantum field theory can only be studied theoretically in black holes, it can
be tested in controlled laboratory experiments. Typically, a fluid accelerating
from sub- to supersonic speed will create an effectively curved spacetime for
the acoustic field, with an apparent horizon where the speed of the fluid
equals the speed of sound. Here we create effective curved spacetimes with a
quantum fluid of light, with smooth and steep acoustic horizons and various
supersonic fluid speeds. We use a recently developed spectroscopy method to
measure the spectrum of acoustic excitations on these spacetimes, thus
observing negative energy modes in the supersonic regions. This demonstrates
the potential of quantum fluids of light for the study of field theories on
curved spacetimes.Comment: 5 pages, 3 figure
Treatment of osteogenesis imperfecta with intravenous pamidronate in pediatric patients: comparison between a single-day infusion twice a year protocol with other regimens described in the literature
A trypsin-like serine protease is involved in pseudorabies virus invasion through the basement membrane barrier of porcine nasal respiratory mucosa
Several alphaherpesviruses breach the basement membrane during mucosal invasion. In the present study, the role of proteases in this process was examined. The serine protease-specific inhibitor AEBSF inhibited penetration of the basement membrane by the porcine alphaherpesvirus pseudorabies virus (PRV) by 88.1% without affecting lateral spread. Inhibitors of aspartic-, cysteine-, and metalloproteases did not inhibit viral penetration of the basement membrane. Further analysis using the Soybean Type I-S trypsin inhibitor for the serine protease subcategory of trypsin-like serine proteases resulted in a 96.9% reduction in plaque depth underneath the basement membrane. These data reveal a role of a trypsin-like serine protease in PRV penetration of the basement membrane
Spectrum of collective excitations of a quantum fluid of polaritons
We use a recently developed high-resolution coherent probe spectroscopy
method to investigate the dispersion of collective excitations of a polaritonic
quantum fluid. We measure the dispersion relation with high energy and
wavenumber resolution, which allows us to determine the speed of sound in the
fluid and to evidence the contribution of an excitonic reservoir. We report on
the generation of collective excitations at negative energies, on the ghost
branch of the dispersion curve. Precursors of dynamical instabilities are also
identified. Our methods open the way to the precise study of quantum
hydrodynamics of quantum fluids of light
Serum levels and removal by haemodialysis and haemodiafiltration of tryptophan-derived uremic toxins in ESKD patients
Tryptophan is an essential dietary amino acid that originates uremic toxins that contribute to end-stage kidney disease (ESKD) patient outcomes. We evaluated serum levels and removal during haemodialysis and haemodiafiltration of tryptophan and tryptophan-derived uremic toxins, indoxyl sulfate (IS) and indole acetic acid (IAA), in ESKD patients in different dialysis treatment settings. This prospective multicentre study in four European dialysis centres enrolled 78 patients with ESKD. Blood and spent dialysate samples obtained during dialysis were analysed with high-performance liquid chromatography to assess uremic solutes, their reduction ratio (RR) and total removed solute (TRS). Mean free serum tryptophan and IS concentrations increased, and concentration of IAA decreased over pre-dialysis levels (67%, 49%, -0.8%, respectively) during the first hour of dialysis. While mean serum total urea, IS and IAA concentrations decreased during dialysis (-72%, -39%, -43%, respectively), serum tryptophan levels increased, resulting in negative RR (-8%) towards the end of the dialysis session (p < 0.001), despite remarkable Trp losses in dialysate. RR and TRS values based on serum (total, free) and dialysate solute concentrations were lower for conventional low-flux dialysis (p < 0.001). High-efficiency haemodiafiltration resulted in 80% higher Trp losses than conventional low-flux dialysis, despite similar neutral Trp RR values. In conclusion, serum Trp concentrations and RR behave differently from uremic solutes IS, IAA and urea and Trp RR did not reflect dialysis Trp losses. Conventional low-flux dialysis may not adequately clear Trp-related uremic toxins while high efficiency haemodiafiltration increased Trp losses
Comparative analysis of replication characteristics of BoHV-1 subtypes in bovine respiratory and genital mucosa explants: a phylogenetic enlightenment
In general, members of the Alphaherpesvirinae use the epithelium of the upper respiratory and/or genital tract as a preferential site for primary replication. Bovine herpesvirus type 1 (BoHV-1) may replicate at both sites and cause two major clinical entities designated as infectious bovine rhinotracheitis (IBR) and infectious pustular vulvovaginitis/balanoposthitis (IPV/IPB) in cattle. It has been hypothesized that subtype 1.1 invades preferentially the upper respiratory mucosa whereas subtype 1.2 favors replication at the peripheral genital tract. However, some studies are in contrast with this hypothesis. A thorough study of primary replication at both mucosae could elucidate whether or not different BoHV-1 subtypes show differences in mucosa tropism. We established bovine respiratory and genital organ cultures with emphasis on maintenance of tissue morphology and viability during in vitro culture. In a next step, bovine respiratory and genital mucosa explants of the same animals were inoculated with several BoHV-1 subtypes. A quantitative analysis of viral invasion in the mucosa was performed at 0 h, 24 h, 48 h and 72 h post inoculation (pi) by measuring plaque latitude and penetration depth underneath the basement membrane. All BoHV-1 subtypes exhibited a more profound invasion capacity in respiratory tissue compared to that in genital tissue at 24 h pi. However, at 24 h pi plaque latitude was found to be larger in genital tissue compared to respiratory tissue and this for all subtypes. These similar findings among the different subtypes take the edge off the belief of the existence of specific mucosa tropisms of different BoHV-1 subtypes
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