Levitated droplet dye laser

We present the first observation, to our knowledge, of lasing from a levitated, dye droplet. The levitated droplets are created by computer controlled pico-liter dispensing into one of the nodes of a standing ultrasonic wave (100 kHz), where the droplet is trapped. The free hanging droplet forms a high quality optical resonator. Our 750 nL lasing droplets consist of Rhodamine 6G dissolved in ethylene glycol, at a concentration of 0.02 M. The droplets are optically pumped at 532 nm light from a pulsed, frequency doubled Nd:YAG laser, and the dye laser emission is analyzed by a fixed grating spectrometer. With this setup we have achieved reproducible lasing spectra in the visible wavelength range from 610 nm to 650 nm. The levitated droplet technique has previously successfully been applied for a variety of bio-analytical applications at single cell level. In combination with the lasing droplets, the capability of this high precision setup has potential applications within highly sensitive intra-cavity absorbance detection.Comment: 6 pages including 3 figure

Calculation of the singlet-triplet gap of the antiferromagnetic Heisenberg Model on the ladder

The ground state energy and the singlet-triplet energy gap of the antiferromagnetic Heisenberg model on a ladder is investigated using a mean field theory and the density matrix renormalization group. Spin wave theory shows that the corrections to the local magnetization are infinite. This indicates that no long range order occurs in this system. A flux-phase state is used to calculate the energy gap as a function of the transverse coupling, $J_\perp$, in the ladder. It is found that the gap is linear in $J_\perp$ for $J_\perp\gg 1$ and goes to zero for $J_\perp\to 0$. The mean field theory agrees well with the numerical results.Comment: 11pages,6 figures (upon request) Revtex 3.0, Report#CRPS-94-0

Current developments in gene therapy for amyotrophic lateral sclerosis.

INTRODUCTION: Amyotrophic lateral sclerosis (ALS) is a devastating adult neurodegenerative disorder characterized by motor neuron degeneration and death around 3 years from onset. So far, riluzole is the only treatment available, although it only offers a slight increase in survival. The complex etiology of ALS, with several genes able to trigger the disease, makes its study difficult. Areas covered: RNA-mediated or protein-mediated toxic gain-of-function leading to motor neuron degeneration appears to be likely common pathogenic mechanisms in ALS. Consequently, gene therapy technologies to reduce toxic RNA and/or proteins and to protect motor neurons by modulating gene expression are at the forefront of the field. Here, we review the most promising scientific advances, paying special attention to the successful treatments tested in animal models as well as analyzing relevant gene therapy clinical trials. Expert opinion: Despite broad advances in target gene identification in ALS and advances in gene therapy technologies, a successful gene therapy for ALS continues to elude researchers. Multiple hurdles encompassing technical, biological, economical and clinical challenges must be overcome before a therapy for patients becomes available. Optimism remains due to positive results obtained in several in vivo studies demonstrating significant disease amelioration in animal models of ALS

Synthesis of diverse glycosylphosphatidylinositol glycans from toxoplasma gondii and their application as vaccines and diagnostics

The present invention relates to the synthesis of GPI-related surface antigens of the parasite Toxoplasma gondii (T. gondii) and the resulting products obtained. These synthetic compounds are suitable for diagnosis of toxoplasmosis, as well as vaccine against toxoplasmosis, a diseases caused by infection with T. gondii

Anisotropic two-dimensional Heisenberg model by Schwinger-boson Gutzwiller projected method

Two-dimensional Heisenberg model with anisotropic couplings in the $x$ and $y$ directions ($J_x \neq J_y$) is considered. The model is first solved in the Schwinger-boson mean-field approximation. Then the solution is Gutzwiller projected to satisfy the local constraint that there is only one boson at each site. The energy and spin-spin correlation of the obtained wavefunction are calculated for systems with up to $20 \times 20$ sites by means of the variational Monte Carlo simulation. It is shown that the antiferromagnetic long-range order remains down to the one-dimensional limit.Comment: 15 pages RevTex3.0, 4 figures, available upon request, GWRVB8-9

A Renormalization Group Method for Quasi One-dimensional Quantum Hamiltonians

A density-matrix renormalization group (DMRG) method for highly anisotropic two-dimensional systems is presented. The method consists in applying the usual DMRG in two steps. In the first step, a pure one dimensional calculation along the longitudinal direction is made in order to generate a low energy Hamiltonian. In the second step, the anisotropic 2D lattice is obtained by coupling in the transverse direction the 1D Hamiltonians. The method is applied to the anisotropic quantum spin half Heisenberg model on a square lattice.Comment: 4 pages, 4 figure

The Association of Cerebral Palsy with Other Disability in Children with Perinatal Arterial Ischemic Stroke

The association of cerebral palsy with other disabilities in children with perinatal stroke has not been well-studied. We examined this association in 111 children with perinatal stroke: 67 with neonatal presentation, and 44 with delayed presentation. Seventy-six children (68%) had cerebral palsy, which was hemiplegic in 66 and tri- or quadriplegic in 10. Fifty-five (72%) children with cerebral palsy had at least one other disability: 45 (59%) had a cognitive/speech impairment (moderate-severe in 20), and 36 (47%) had epilepsy (moderate-severe in 11). In children with neonatal presentation, cerebral palsy was associated with epilepsy (P = 0.0076) and cognitive impairment (P = 0.0001). These associations could not be tested in children with delayed presentation because almost all children in this group had cerebral palsy. In another analysis with multivariate logistic regression for children with cerebral palsy, children who had both neonatal presentation and history of cesarean-section delivery were more likely to have epilepsy (P = 0.001). Children with cerebral palsy after perinatal stroke who had neonatal presentation were more likely to have severe cognitive impairment (odds ratio, 7.78; 95% confidence interval, 1.80-47.32) or severe epilepsy (odds ratio, 6.64; 95% confidence interval, 1.21-69.21) than children with delayed presentation. Children with cerebral palsy after perinatal stroke are likely to have an additional disability; those with neonatal presentation are more likely to have a severe disability

Lasing from single, stationary, dye-doped glycerol/water microdroplets located on a superhydrophobic surface

We report laser emission from single, stationary, Rhodamine B-doped glycerol/water microdroplets located on a superhydrophobic surface. In the experiments, a pulsed, frequency-doubled Nd:YAG laser operating at 532 nm was used as the excitation source. The microdroplets ranged in diameter from a few to 20 um. Lasing was achieved in the red-shifted portion of the dye emission spectrum with threshold fluences as low as 750 J/cm2. Photobleaching was observed when the microdroplets were pumped above threshold. In certain cases, multimode lasing was also observed and attributed to the simultaneous lasing of two modes belonging to different sets of whispering gallery modes.Comment: to appear in Optics Communication

Endoscopic Evaluation and Management of Gastrointestinal Bleeding in Patients with Ventricular Assist Devices

The optimal diagnostic approach and yield for gastrointestinal bleeding (GIB) in patients with ventricular assist devices (VAD) are unknown. We explored the etiology of bleeding and yield of upper and lower endoscopy, balloon-assisted enteroscopy, and video capsule endoscopy in the evaluation of GIB in patients with VADs. Methods. All VAD patients with overt gastrointestinal bleeding and drop in hematocrit from April 1, 2000 to July 31, 2008 were retrospectively reviewed. The endoscopic evaluation of each episode was recorded. Overall yield of EGD, colonoscopy, balloon-assisted, and video capsule endoscopy were evaluated. Results. Thirty-six bleeding episodes occurred involving 20 patients. The site of GIB was identified in 32/36 episodes (88.9%), and the etiology of bleeding was determined in 30/36 cases (83.3%). Five VAD patients underwent VCE. The VCE exams demonstrated a high yield with 80% of exams identifying the etiology of GIB. Endoscopic intervention was successful in 8/9 attempts. No adverse events were recorded. Two patients required surgical intervention for GIB. Conclusion. Upper, lower, video capsule, and balloon-assisted enteroscopies are safe and demonstrate a high yield in the investigation of gastrointestinal bleeding in VAD patients. Medical centers caring for VAD patients should employ a standardized protocol to optimize endoscopic evaluation and intervention