Surface chemistry of 2,3-dibromosubstituted norbornadiene/quadricyclane as molecular solar thermal energy storage system on Ni(111).

Dwindling fossil fuels force humanity to search for new energy production routes. Besides energy generation, its storage is a crucial aspect. One promising approach is to store energy from the sun chemically in strained organic molecules, so-called molecular solar thermal (MOST) systems, which can release the stored energy catalytically. A prototypical MOST system is norbornadiene/quadricyclane (NBD/QC) whose energy release and surface chemistry need to be understood. Besides important key parameters such as molecular weight, endergonic reaction profiles, and sufficient quantum yields, the position of the absorption onset of NBD is crucial to cover preferably a large range of sunlight's spectrum. For this purpose, one typically derivatizes NBD with electron-donating and/or electron-accepting substituents. To keep the model system simple enough to be investigated with photoemission techniques, we introduced bromine atoms at the 2,3-position of both compounds. We study the adsorption behavior, energy release, and surface chemistry on Ni(111) using high-resolution X-ray photoelectron spectroscopy (HR-XPS), UV photoelectron spectroscopy, and density functional theory calculations. Both Br2-NBD and Br2-QC partially dissociate on the surface at ∼120 K, with Br2-QC being more stable. Several stable adsorption geometries for intact and dissociated species were calculated, and the most stable structures are determined for both molecules. By temperature-programmed HR-XPS, we were able to observe the conversion of Br2-QC to Br2-NBD in situ at 170 K. The decomposition of Br2-NBD starts at 190 K when C-Br bond cleavage occurs and benzene and methylidene are formed. For Br2-QC, the cleavage already occurs at 130 K when cycloreversion to Br2-NBD sets in.

Planck distribution of phonons in a Bose-Einstein condensate.

The Planck distribution of photons emitted by a blackbody led to the development of quantum theory. An analogous distribution of phonons should exist in a Bose-Einstein condensate. We observe this Planck distribution of thermal phonons in a 3D condensate. This observation provides an important confirmation of the basic nature of the condensate's quantized excitations. In contrast to the bunching effect, the density fluctuations are seen to increase with increasing temperature. This is due to the nonconservation of the number of phonons. In the case of rapid cooling, the phonon temperature is out of equilibrium with the surrounding thermal cloud. In this case, a Bose-Einstein condensate is not as cold as previously thought. These measurements are enabled by our in situ k-space technique.

Observing atom bunching by the Fourier slice theorem.

By a novel reciprocal space analysis of the measurement, we report a calibrated in situ observation of the bunching effect in a 3D ultracold gas. The calibrated measurement with no free parameters confirms the role of the exchange symmetry and the Hanbury Brown-Twiss effect in the bunching. Also, the enhanced fluctuations of the bunching effect give a quantitative measure of the increased isothermal compressibility. We use 2D images to probe the 3D gas, using the same principle by which computerized tomography reconstructs a 3D image of a body. The powerful reciprocal space technique presented is applicable to systems with one, two, or three dimensions.

Phonon dispersion relation of an atomic Bose-Einstein condensate.

We measure the time oscillations of a freely evolving standing wave of phonons in a Bose-Einstein condensate. We present the technique of short Bragg pulses, which stimulates the standing wave. The subsequent oscillations are observed in situ. The frequency of the oscillations gives the dispersion relation, the amplitude gives the static structure factor, and the decay gives the dephasing time. The new technique gives orders of magnitude more sensitivity than Bragg spectroscopy, allowing for the observation of deviations from the local density approximation. Specifically, it is seen that the phonons undergo a transition from three dimensions to one dimension, when their wavelength becomes longer than the transverse radius of the condensate. The one-dimensional regime contains an inflection point in the dispersion relation, a decrease in the superfluid critical velocity, a minimum in the group velocity, and an increase in the lifetime of the standing wave oscillations.

The a.c. and d.c. Josephson effects in a Bose-Einstein condensate.

The alternating- and direct-current (a.c. and d.c.) Josephson effects were first discovered in a system of two superconductors, the macroscopic wavefunctions of which are weakly coupled via a tunnelling barrier. In the a.c. Josephson effect, a constant chemical potential difference (voltage) is applied, which causes an oscillating current to flow through the barrier. Because the frequency is proportional to the chemical potential difference only, the a.c. Josephson effect serves as a voltage standard. In the d.c. Josephson effect, a small constant current is applied, resulting in a constant supercurrent flowing through the barrier. In a sense, the particles do not 'feel' the presence of the tall tunnelling barrier, and flow freely through it with no driving potential. Bose-Einstein condensates should also support Josephson effects; however, while plasma oscillations have been seen in a single Bose-Einstein condensate Josephson junction, the a.c. Josephson effect remains elusive. Here we observe the a.c. and d.c. Josephson effects in a single Bose-Einstein condensate Josephson junction. The d.c. Josephson effect has been observed previously only in superconducting systems; in our study, it is evident when we measure the chemical potential-current relation of the Bose-Einstein condensate Josephson junction. Our system constitutes a trapped-atom interferometer with continuous readout, which operates on the basis of the a.c. Josephson effect. In addition, the measured chemical potential-current relation shows that the device is suitable for use as an analogue of the superconducting quantum interference device, which would sense rotation.

Prospective endoscopic evaluation for gastrointestinal graft-versus-host disease: determination of the best diagnostic approach.

The best endoscopic diagnostic strategy for gastrointestinal (GI) graft-versus-host disease (GVHD) is unknown. Over a 48-month period, all patients with unexplained diarrhea at risk for acute gastrointestinal GVHD were prospectively identified. Acute GVHD was defined as symptoms and histologic evidence of GVHD occurring within 100 days of transplant or donor lymphocyte infusion (DLI). Colonoscopy was performed with multiple biopsies of the ileum, right colon and rectosigmoid colon. Next, upper endoscopy with duodenal and random gastric biopsies of both antrum and body were performed. All biopsies were evaluated for GVHD by an experienced GI pathologist. Over the study period, 24 patients (mean age 37 years; 62.5% male) were evaluated. The median time from transplantation or DLI was 30.5 days. The biopsy site with the highest yield was the distal colon (82%). A combination of upper endoscopy with sigmoidoscopy and colonoscopy with ileal biopsies were equivalent ( approximately 94%). In patients with diarrhea at risk for GVHD, biopsies of the distal colon had the highest diagnostic yield suggesting the importance of sigmoidoscopy and biopsy. Colonoscopy and ileoscopy or flexible sigmoidoscopy plus upper endoscopy had the highest diagnostic yields.

High sensitivity phonon spectroscopy of Bose-Einstein condensates using matter-wave interference.

We study low-momentum excitations of a Bose-Einstein condensate using a novel matter-wave interference technique. In time-of-flight expansion images we observe strong matter-wave fringe patterns. The fringe visibility is a sensitive spectroscopic probe of in-trap phonons and is explained by use of a Bogoliubov excitation projection method applied to the rescaled order parameter of the expanding condensate. Gross-Pitaevskii simulations agree with the experimental data and confirm the validity of the theoretical interpretation. We show that the high sensitivity of this detection scheme gives access to the quantized quasiparticle regime.

Three-wave mixing of bogoliubov quasiparticles in a bose-einstein condensate.

A dressed basis is used to calculate the dynamics of three-wave mixing between Bogoliubov quasiparticles in a Bose condensate. Because of the observed oscillations between different momentum modes, an energy splitting, analogous to the optical Mollow triplet, appears in the Beliaev damping spectrum of the excitations from the oscillating modes.

Bragg spectroscopy of the multibranch Bogoliubov spectrum of elongated Bose-Einstein condensates.

We measure the response of an elongated Bose-Einstein condensate to a two-photon Bragg pulse. If the duration of the pulse is long, the total momentum transferred to the condensate exhibits a nontrivial behavior which reflects the structure of the underlying Bogoliubov spectrum. It is thus possible to perform a spectroscopic analysis in which axial phonons with a different number of radial nodes are resolved. The local density approximation is shown to fail in this regime, while the observed data agree well with the results of simulations based on the numerical solution of the Gross-Pitaevskii equation.

Vancomycin-resistant enterococci: 15 years and counting.

We review the history of vancomycin-resistant enterococci (VRE) and propose a causal model illustrating the roles of exposure to VRE reservoirs, patient characteristics, antimicrobial exposure, and prevalence of VRE in the progression from potential VRE reservoirs to active disease in hospitalized patients. Differences in VRE colonization and VRE infection are discussed with respect to hospital surveillance methodology and implications for interventions. We further document clonal transmission of VRE in a large, urban, teaching hospital and demonstrate VRE susceptibility to a wide array of antimicrobial agents. This model can guide the identification of mutable factors that are focal points for intervention.

Beliaev damping of quasiparticles in a Bose-Einstein condensate.

We report a measurement of the suppression of collisions of quasiparticles with ground state atoms within a Bose-Einstein condensate at low momentum. These collisions correspond to Beliaev damping of the excitations, in the previously unexplored regime of the continuous quasiparticle energy spectrum. We use a hydrodynamic simulation of the expansion dynamics, with the Beliaev damping cross section, in order to confirm the assumptions of our analysis.

Excitation spectrum of a Bose-Einstein condensate.

We report a measurement of the excitation spectrum omega(k) and the static structure factor S(k) of a Bose-Einstein condensate. The excitation spectrum displays a linear phonon regime, as well as a parabolic single-particle regime. The linear regime provides an upper limit for the superfluid critical velocity, by the Landau criterion. The excitation spectrum agrees well with the Bogoliubov spectrum in the local density approximation, even close to the long-wavelength limit of the region of applicability. Feynman's relation between omega(k) and S(k) is verified, within an overall constant.

Lethal pulmonary hypoplasia after in-utero myelomeningocele repair.

BACKGROUND: In-utero surgical repair of fetal myelomeningocele has been performed as a means to improve the postnatal condition of affected infants. CASE: A nulliparous woman underwent in-utero surgical repair of a fetal lumbosacral myelomeningocele at 24 weeks' gestation. Her postoperative convalescence was complicated by pulmonary edema, abdominal pain, chronic oligohydramnios, and preterm labor. The infant was delivered by cesarean at 33 weeks' gestation, but expired from respiratory distress caused by pulmonary hypoplasia at 9 hours of age. CONCLUSION: Until the benefits of in-utero repair of fetal myelomeningoceles are determined by well-controlled clinical trials, this technique remains investigational. Physicians and their patients who are considering this procedure must be fully aware of the potential risks that can occur.

Spontaneous coronary artery dissection associated with cocaine use: a case report and brief review.

Isolated, spontaneous dissection of the coronary arteries in the absence of trauma is an unusual but well-documented occurrence. Fewer than 50 cases have been reported in males in the English language literature, and only one case, nonfatal, was associated with cocaine use. We present the second overall and the first fatal case of cocaine-associated spontaneous coronary artery dissection and a brief review of the literature on coronary dissection and the cardiovascular effects of cocaine use. The mechanism of cocaine's toxicity on the heart and vasculature is complex, multifactorial, and predominantly related to cocaine's adrenergic properties. The increased arterial blood pressure from cocaine's inotropic and chronotropic effects combined with its direct vasoconstrictive effect leads to increased shear forces on the coronary endothelium. This elevated stress may be responsible for the formation of an intimal tear and the subsequent dissection of the coronary artery. If the dissected portion of the arterial wall is displaced enough to significantly occlude the true lumen, infarction can result. In light of this possibility, coronary artery dissection must be considered in young patients presenting with symptoms of cardiac ischemia and a history of cocaine use.

[Laser canaliculoplasty]. / Lasercanaliculoplastik.

BACKGROUND: Laser canalicular plastic surgery using the erbium-YAG laser is a new method for treating canaliculus stenosis. We compared results of this method with those of conventional surgical operations on canaliculi. PATIENTS AND METHODS: Between 1996 and 1998 a total of 44 cases of symptomatic canaliculus stenosis were treated by laser. An erbium-YAG laser with a maximum power of 100 mJ was used in conjunction with a sapphire fiber 3 cm long and 325 microns in diameter. Endoscopic diagnosis of the other parts of the lacrimal passage was carried out before and after laser treatment and after tubular intubation. After an average of 12 months the results were assessed via questionnaires and follow-up examinations. RESULTS: The success rate for reducing epiphora was 67%. Overall 86% of patients reported an improvement in canaliculus communis stenosis. CONCLUSIONS: Laser canalicular plasty as minimally invasive surgical treatment is an excellent surgical method for treating point-focal, noninflammatory canalicular stenosis.

[Endoscopic laser dacryoplasty. Methodology and outcome after 3 months]. / Endoskopische Laserdakryoplastik. Methodik und Ergebnisse nach drei Monaten.

BACKGROUND: After performing endoscopy of the lacrimal passage, the endoscopic system can be connected to an erbium-YAG laser if the indications are appropriate. MATERIALS AND METHODS: In a bi-center study we performed laser dacryoplasty in 53 cases out of 261 endoscopy procedures (18 stenoses of the canaliculi, 19 stenoses of the sac, 9 stenoses of the nasolacrimal duct, 9 restenoses following DCR). In 35 cases an examination was done and in all 53 cases the results were obtained by means of a questionnaire. RESULTS: Epiphora and irrigation were improved in more than 75%. CONCLUSION: Suitable indications are small stenoses in the sac or duct membranes following DCR. Laser dacryoplasty is a promising method, but more studies still need to be conducted to obtain long-term results. The technical system must also still be improved to make it easier to handle.

The unipolar Shigella surface protein IcsA is targeted directly to the bacterial old pole: IcsP cleavage of IcsA occurs over the entire bacterial surface.

Shigella flexneri is an intracellular pathogen that is able to move within the cytoplasm of infected cells by the continual assembly of actin onto one pole of the bacterium. IcsA, an outer membrane protein, is localized to the old pole of the bacterium and is both necessary and sufficient for actin assembly. IcsA is slowly cleaved from the bacterial surface by the protease IcsP (SopA). Absence of IcsP leads to an alteration in the distribution of surface IcsA, such that the polar cap is maintained and some IcsA is distributed along the lateral walls of the bacillus. The mechanism of unipolar localization of IcsA and the role of IcsP in its unipolar localization are incompletely understood. Here, we demonstrate that cleavage of IcsA occurs exclusively in the outer membrane and that IcsP is localized to the outer membrane. In addition, we show that IcsA at the old pole is susceptible to cleavage by IcsP and that native IcsP is active at the pole. Taken together, these data indicate that IcsP cleaves IcsA over the entire bacterial surface. Finally, we show that, immediately after induction from a tightly regulated promoter, IcsA is expressed exclusively at the old pole in both the icsP- icsA- and the icsA- background. These data demonstrate that unipolar localization of IcsA results from its direct targeting to the pole, followed by its diffusion laterally in the outer membrane.

[Dacryoendoscopy--current status]. / Dakryoendoskopie--gegenwärtiger Stand.

UNLABELLED: In the years from 1995 to 1997 in the eyeclinic of Darmstadt and the eyeclinic of the St. Josef Hospital Hagen 261 dacryoendoscopies were done in a bicentrical study. PATIENTS AND METHODS: A dacryoendoscopy was done in 261 patients with an average age of 46.6 years (143 women, 93 men and 25 children). In dependance of the assessment of the mucosa conditions intraoperatively in all 261 cases the planed operative strategy was checked and if needed changed. As following surgical interventions of the lacrimal system were seen 70 cases of dacryocystorhinostomia externa, 138 cases of intubation of the lacrimal drainage system and 53 cases of laserdacryoplastic. RESULTS: The dacryoendoscopy had succeeded as method for the assessment of the mucosa conditions [5, 6]. In a study of 261 dacryoendoscopies an examination of the mucosa was possible in every case. No complications were seen while dacryoendoscopy. With help of the dacryoendoscopy the planed operative strategy was determined. Therefore we had the possibility to choose a minimal invasive operation-procedure in 53 cases. CONCLUSIONS: The dacryoendoscopy is a new important diagnostic development in diagnosis of diseases of the lacrimal drainage system. With help of better developed endoscopy-systems a much better quality of the picture is attainable. The results of the dacryoendoscopy offer the possibility to check the preoperative indication and to optimate the surgical treatment. At last only with help of the dacryoendoscopy these findings could be ascertained in which case a laserdacryoplastic is senseful.