Thermoacoustic Soret separation.

In a fluid mixture in a channel with an axial time-averaged temperature gradient, high-amplitude oscillating flow can greatly increase the axial flux of thermal diffusion (Soret) separation of the components of the mixture. The enhancement occurs when the oscillating lateral temperature gradient greatly exceeds the axial gradient, causing a large oscillating concentration that can be favorably time-phased with the oscillating flow. This process can occur even with a negligible pressure oscillation or with a negligible temperature response to pressure, as is the case in most liquid solutions. The thermal boundary condition imposed by realistic solids on thermoacoustic liquids is imperfect, adding mathematical complications that are absent for typical gases, for which the solid surface is temporally isothermal. Compared with gas mixtures, the high Lewis number in typical liquid solutions reduces the separation flux associated with the time-averaged temperature gradient, but it also reduces the remixing associated with the time-averaged mole-fraction gradient. For large enough channels, the second-law separation efficiency is only slightly reduced from that of steady liquid Soret separation.

Proton Compton Scattering from Linearly Polarized Gamma Rays.

Differential cross sections for Compton scattering from the proton have been measured at scattering angles of 55°, 90°, and 125° in the laboratory frame using quasimonoenergetic linearly (circularly) polarized photon beams with a weighted mean energy value of 83.4 MeV (81.3 MeV). These measurements were performed at the High Intensity Gamma-Ray Source facility at the Triangle Universities Nuclear Laboratory. The results are compared to previous measurements and are interpreted in the chiral effective field theory framework to extract the electromagnetic dipole polarizabilities of the proton, which gives α_{E1}^{p}=13.8±1.2_{stat}±0.1_{BSR}±0.3_{theo},ß_{M1}^{p}=0.2∓1.2_{stat}±0.1_{BSR}∓0.3_{theo} in units of 10^{-4} fm^{3}.

High-purity thermoacoustic isotope enrichment.

In a tube many wavelengths long, thermoacoustic separation of a gas mixture can produce very high purities. A flexible wall allows a spatially continuous supply of acoustic power into such a long tube. Coiling the tube and immersing it in a fluid lets a single-wavelength, circulating, traveling pressure wave in the fluid drive all the wavelengths in the tube wall and gas. Preliminary measurements confirm many aspects of the concept with neon ((20)Ne and (22)Ne) and highlight some challenges of practical implementation.

Negative refraction and the spectral filtering of terahertz radiation by a photonic crystal prism.

We demonstrate how micromachined photonic crystals can be used to negatively refract terahertz frequency light. The photonic crystals, which are constructed from conventional dielectric materials, manipulate the incident beam via interaction with their photonic bands. Consequently, we show that different components of a broadband beam incident on the structure may be positively or negatively refracted, depending upon its frequency and that the structure can be used as an effective spectral filter of THz radiation.

Helping the general physician to improve outcomes after PEG insertion: how we changed our practice.

During their careers, most general physicians are involved in the decision-making process for patients that potentially require percutaneous endoscopic gastrostomy (PEG) insertion. However, poor patient selection and less than favourable outcomes are frequently observed in this group. With the aim of identifying and addressing the underlying issues, the PEG service at University Hospital Llandough was radically changed over an eight-year period. The development of a nurse-led pre-assessment service and design of a specific referral form was successful in reducing the number of PEG referrals and consequently the 30-day mortality rate. Furthermore, the educational and training needs of general physicians of all grades regarding the issues surrounding PEG placement were identified and addressed at formal teaching sessions. A combination of these factors has positively impacted on our service, with more appropriate patient selection and a reduced 30-day mortality rate.

The pulse tube and the pendulum.

An inverted pulse tube in which gravity-driven convection is suppressed by acoustic oscillations is analogous to an inverted pendulum that is stabilized by high-frequency vibration of its pivot point. Gravity acts on the gas density gradient arising from the end-to-end temperature gradient in the pulse tube, exerting a force proportional to that density gradient, tending to cause convection when the pulse tube is inverted. Meanwhile, a nonlinear effect exerts an opposing force proportional to the square of any part of the density gradient that is not parallel to the oscillation direction. Experiments show that convection is suppressed when the pulse-tube convection number N(ptc)=omega(2)a(2)DeltaT/T(avg)/[g(alphaD sin theta-L cos theta)] is greater than 1 in slender tubes, where omega is the radian frequency of the oscillations, a is their amplitude, DeltaT is the end-to-end temperature difference, T(avg) is the average absolute temperature, g is the acceleration of gravity, L is the length of the pulse tube and D is its diameter, alpha is about 1.5, and the tip angle theta ranges from 90 degrees for a horizontal tube to 180 degrees for an inverted tube. Theory suggests that the temperature dependence should be DeltaT/T(avg) instead of DeltaT/T(avg).

Thermoacoustic mixture separation with an axial temperature gradient.

The theory of thermoacoustic mixture separation is extended to include the effect of a nonzero axial temperature gradient. The analysis yields a new term in the second-order mole flux that is proportional to the temperature gradient and to the square of the volumetric velocity and is independent of the phasing of the wave. Because of this new term, thermoacoustic separation stops at a critical temperature gradient and changes direction above that gradient. For a traveling wave, this gradient is somewhat higher than that predicted by a simple four-step model. An experiment tests the theory for temperature gradients from 0 to 416 K/m in 50-50 He-Ar mixtures.

Coeliac disease and primary hyperparathyroidism: an association?

Primary hyperparathyroidism may present with non-specific symptoms, and this may be one reason why patients with coeliac disease fail to improve despite compliance with a gluten-free diet. Seven case reports of primary hyperparathyroidism due to sporadic adenoma occurring in a series of 310 patients with coeliac disease are presented, highlighting the importance of looking for this condition in this population group. A prevalence of primary hyperparathyroidism of 2.3% in this series suggests a significant association between hyperparathyroidism and coeliac disease; most studies have indicated a prevalence of 3 in 1000 in the general population, although one study found that it may be as high as 21 in 1000 in women aged 55-75 years. The average age of patients in our series was 59 years and all but one were women. Further studies are needed to establish a possible association between primary hyperparathyroidism and coeliac disease.

Does endoscopy diagnose early gastrointestinal cancer in patients with uncomplicated dyspepsia?

BACKGROUND: Recent guidelines from NICE have proposed that open access gastroscopy is largely limited to patients with "alarm" symptoms. AIMS AND METHODS: This study reviewed the outcome of all our patients with verified oesophageal or gastric carcinoma who presented with uncomplicated dyspepsia to see if endoscopic investigation is warranted in this group. All patients with histologically verified upper gastrointestinal (GI) cancers who presented over a period from 1998 to 2002 were identified. Their presenting symptoms, treatment, and outcome were analysed. RESULTS: 228 upper GI cancers (119 oesophageal, 109 gastric; mean age 72 years (29-99 years); 130 male, 82 female) were identified in 11 145 endoscopies performed. Only 14 patients (6.2%) presented without alarm symptoms; three patients were under 55 years of age and all had gastric carcinoma-one of these had chronic diarrhoea only. Eleven had dyspepsia or reflux symptoms only, and two were under surveillance for Barrett's oesophagus. Only five patients had a curative surgical resection and are still alive two-six years from diagnosis. A sixth patient had a curative operation but died of a cerebrovascular accident one year later. The remaining eight patients unfortunately had either metastatic disease or comorbidity, which precluded surgery. All of these died within two years of diagnosis, mean survival 10 months. CONCLUSION: Only five patients with dyspepsia and no alarm symptoms had resectable upper GI malignancies over a four year period. Limiting open access gastroscopy to those with alarm features only would "miss" a small number of patients who have curable upper GI malignancy.

A cascade thermoacoustic engine.

A cascade thermoacoustic engine is described, consisting of one standing-wave stage plus two traveling-wave stages in series. Most of the acoustic power is produced in the efficient traveling-wave stages. The straight-line series configuration is easy to build and allows no Gedeon streaming. The engine delivers up to 2 kW of acoustic power, with an efficiency (the ratio of acoustic power to heater power) of up to 20%. An understanding of the pressure and volume-velocity waves is very good. The agreement between measured and calculated powers and temperatures is reasonable. Some of the measured thermal power that cannot be accounted for by calculation can be attributed to Rayleigh streaming in the two thermal buffer tubes with the largest aspect ratios. A straightforward extension of this work should yield cascade thermoacoustic engines with efficiencies of around 35-40% of the Carnot efficiency.

Power dissipation and time-averaged pressure in oscillating flow through a sudden area change.

Experiments on oscillating flow at the abrupt transition between a two-dimensional channel and essentially infinite space are presented. It is shown that phenomena associated with the transition are functions of three independent dimensionless parameters including the dimensionless radius rounding the edge of the end of the channel. The effect of each of these three parameters on the time-averaged pressure difference across the transition and the acoustic power dissipation is explored by holding two parameters fixed while varying the third. Evidence is presented that the losses due to oscillatory flow in this geometry are smaller than would be expected from commonly accepted values for steady flow in similar geometry.

An acoustic streaming instability in thermoacoustic devices utilizing jet pumps.

Thermoacoustic-Stirling hybrid engines and feedback pulse tube refrigerators can utilize jet pumps to suppress streaming that would otherwise cause large heat leaks and reduced efficiency. It is desirable to use jet pumps to suppress streaming because they do not introduce moving parts such as bellows or membranes. In most cases, this form of streaming suppression works reliably. However, in some cases, the streaming suppression has been found to be unstable. Using a simple model of the acoustics in the regenerators and jet pumps of these devices, a stability criterion is derived that predicts when jet pumps can reliably suppress streaming.

Thermodynamic efficiency of thermoacoustic mixture separation.

The acoustic power loss in the thermoacoustic mixture-separation process is derived, including the contributions due to a nonzero gradient in concentration. The significance of the gradient-dependent term is discussed. The limiting thermodynamic efficiency of the separation is calculated. Under reasonable circumstances, the efficiency approaches 10(-2) nHnL(delta m/m(avg))2, where nH and nL are the mole fractions of the two components of the mixture, and delta m/m(avg) is the fractional difference between the molar masses of the two components. This efficiency is of the same order of magnitude as that of some other, more conventional separation methods.

Saturation of thermoacoustic mixture separation.

The theory for thermoacoustic mixture separation is extended to include the effects of a nonzero concentration gradient. New data are presented, which are in excellent agreement with this theory. The maximum concentration gradient which may be achieved in a binary mixture of gases through this separation process is intrinsically limited by the fractional pressure amplitude, by the tidal displacement, and by the size of the thermal diffusion ratio. Ordinary diffusion further detracts from the attainable final concentration gradient and can become the dominant remixing process as the cross section of the duct is increased. Rayleigh streaming also works against thermoacoustic separation, and an estimate of the molar flux from streaming is given.

Parity measurements of nuclear levels using a free-electron-laser generated gamma-ray beam.

The quality and intensity of gamma rays at the High Intensity gamma-ray Source are shown to make nuclear resonance fluorescence studies possible at a new level of precision and efficiency. First experiments have been carried out using an intense (10(7) gamma/s) beam of 100% linearly polarized, nearly monoenergetic, gamma rays on the semimagic nucleus (138)Ba. Negative parity quantum numbers have been assigned to 18 dipole excitations of (138)Ba between 5.5 MeV and 6.5 MeV from azimuthal gamma-intensity asymmetries.

Enteric-release glyceryl trinitrate in active Crohn's disease: a randomized, double-blind, placebo-controlled trial.

BACKGROUND: Mucosal ischaemia may contribute to the pathogenesis of Crohn's disease. Microvascular abnormalities have been found in colonic resection specimens, and mucosal levels of constitutive nitric oxide synthase are reduced. AIM: To assess the efficacy of a novel, enteric-release formulation of the nitric oxide donor, glyceryl trinitrate, aimed at increasing the mucosal circulation and relaxing smooth muscle in the affected bowel. METHODS: The trial was randomized, double-blind and placebo-controlled. Baseline disease activity was assessed by a structured symptom diary, with blood tests and a quality of life assessment. Patients with a Crohn's disease activity index of > or = 150 and < 450 were randomized to receive 12 weeks of either glyceryl trinitrate (initially 6 mg twice daily, increasing to 9 mg twice daily after 6 weeks) or an identical placebo. Assessments were repeated at 6 and 12 weeks. RESULTS: Seventy patients (22 male) entered the study; 34 were given glyceryl trinitrate and 36 placebo. At 12 weeks, there were no differences between the treatment groups in terms of Crohn's disease activity index, pain, stool frequency, inflammatory markers or quality of life scores. CONCLUSIONS: Enteric-release glyceryl trinitrate did not benefit patients with mild to moderately active Crohn's disease. Whilst ischaemia may contribute to the pathogenesis of Crohn's disease, our results fail to provide supportive evidence for this hypothesis.

The role of PTF1-P48 in pancreatic acinar gene expression.

The 100-base pair ELA1 transcriptional enhancer drives high level transcription to pancreatic acinar cells of transgenic mice and in transfected pancreatic acinar cells in culture. The A element within the enhancer is the sole positively acting element for acinar specificity. We show that the acinar cell-specific bHLH protein PTF1-P48 and the common bHLH cofactor HEB are part of the PTF1 complex that binds the A element and mediates its activity. Acinar-like activity of the enhancer can be reconstituted in HeLa cells by the introduction of P48, HEB, and the PDX1-containing trimeric homeodomain complex that binds the second pancreatic element of the enhancer. The 5' region of the mouse Ptf1-p48 gene from -12.5 to +0.2 kilobase pairs contains the regulatory information to direct expression in transgenic mice to the pancreas and other organs of the gut that express the endogenous Ptf1-p48 gene. The 5'-flanking sequence contains two activating regions, one of which is specific for acinar cells, and a repressing domain active in non-pancreatic cells. Comparison of the 5'-gene flanking regions of the mouse, rat, and human genes identified conserved sequence blocks containing binding sites for known gut transcription factors within the acinar cell-specific control region.

Vector volume analysis of the lower esophageal sphincter in achalasia and the effect of balloon dilation.

Assessment of the effect of balloon dilation of the lower esophageal sphincter in achalasia currently relies on symptom scores, radiologic studies, or manometry. We have used vector volume analysis which constructs a three-dimensional (3D) pressure profile to examine the effects of balloon dilation on the sphincter. Studies were performed in 26 normal subjects and in 11 patients with achalasia in whom vector volume was determined before and/or after balloon dilation. Vector volume analysis was performed using a multilumen manometry catheter with eight side-reading ports. The catheter was withdrawn through the sphincter using a continuous pull-through technique. A 3D pressure profile was constructed. Vector volume of the lower esophageal sphincter shows a marked radial and linear asymmetry in normal subjects. 3D pressure profiles showed a symmetrical increase in lower esophageal sphincter pressure in untreated achalasia. Mean vector volumes pre and postdilation fell from 254 to 88 cm3 respectively. This was associated with a fall in the mean radial symmetry index from 0.83 to 0.76. Improvement in dysphagia occurred in those patients in whom pressure fell to 15 mmHg or below in at least three adjacent segments. This technique may be a useful tool in the assessment of patients with achalasia and postdilation results may help to predict the long-term outcome of treatment.