Nonlinear optical spectroscopy of diamond surfaces

Second harmonic generation (SHG) and infrared-visible sum frequency generation (SFG) spectroscopies have been shown to be powerful and versatile for studying surfaces with submonolayer sensitivity. They have been used in this work to study bare diamond surfaces and molecular adsorption on them. In particular, infrared-visible SFG as a surface vibrational spectroscopic technique has been employed to identify and monitor in-situ surface bonds and species on the diamond (111) surface. The CH stretch spectra allow us to investigate hydrogen adsorption, desorption, abstraction, and the nature of the hydrogen termination. The C(111) surface dosed with atomic hydrogen was found to be in a monohydride configuration with the hydrogen atoms situated at top-sites. The ratio of the abstraction rate to the adsorption rate was appreciable during atomic hydrogen dosing. Kinetic parameters for thermal desorption of H on C(111) were determined showing a near first-order kinetics. For the fully H-terminated (111) surface, a large (110 cm{sup {minus}1}) anharmonicity and {approximately}19 psec lifetime were measured for the first-excited CH stretch mode. The bare reconstructed C(111)-(2 {times} l) surface showed the presence of CC stretch modes which were consistent with the Pandey {pi}-bonded chain structure. When exposed to the methyl radical, the SFG spectra of the C(111) surface showed features suggesting the presence of adsorbed methyl species. After heating to sufficiently high temperatures, they were converted into the monohydride species. Preliminary results on the hydrogen-terminated diamond (100) surface are also presented

Actors that Unify Threads and Events

There is an impedance mismatch between message-passing concurrency and virtual machines, such as the JVM. VMs usually map their threads to heavyweight OS processes. Without a lightweight process abstraction, users are often forced to write parts of concurrent applications in an event-driven style which obscures control flow, and increases the burden on the programmer. In this paper we show how thread-based and event-based programming can be unified under a single actor abstraction. Using advanced abstraction mechanisms of the Scala programming language, we implemented our approach on unmodified JVMs. Our programming model integrates well with the threading model of the underlying VM

An Atypical Presentation of Acute Macular Neuroretinopathy after Non-Ocular Trauma

Purpose: Acute macular neuroretinopathy (AMN) is a rare clinical entity with an uncertain etiology. We report an atypical case presenting with retinal hemorrhages (RH) and cotton-wool spots (CWS) following non-ocular trauma. Observations: A 49-year-old male presented with an acute onset of a paracentral scotoma in his left eye, immediately following a motor vehicle accident 1 day prior. Fundus findings revealed a unilateral nasal petalloid perifoveal lesion with the tip pointing toward the fovea associated with CWS and RH. Optical coherence tomography demonstrated disruption of the ellipsoid zone. Symptoms and exam findings improved at 2-week follow-up without any intervention, consistent with the natural history of the disease process. Conclusion: We report a rare case of AMN following non-ocular trauma with the unique fundus findings of CWS and RH. This presentation supports the role of ischemia in the retinal deep capillary plexus, of which trauma contributed to the pathophysiological process. Summary: AMN is a rare condition whose pathophysiological process remains speculative. We report an atypical case of AMN, which supports the role of trauma in the pathophysiology of deep retinal capillary plexus compromise

Arts Undergraduate Handbook 2009

PURPOSE: Anemia is associated with poor tumor control. It was previously observed that accelerated radiotherapy combined with carbogen breathing and nicotinamide (ARCON) can correct this adverse outcome in patients with head and neck cancer. The purpose of this study was to validate this observation based on data from a randomized trial. EXPERIMENTAL DESIGN: Of 345 patients with cT2-4 laryngeal cancer, 174 were randomly assigned to accelerated radiotherapy and 171 to ARCON. Hemoglobin levels, measured before treatment, were defined as low when <7.5 mmol/L for women and <8.5 mmol/L for men. The hypoxia marker pimonidazole was used to assess the oxygenation status in tumor biopsies. Data were analyzed 2 years after inclusion of the last patient. RESULTS: Pretreatment hemoglobin levels were available and below normal in 27 of 173 (16%) accelerated radiotherapy and 27 of 167 (16%) ARCON patients. In patients with normal pretreatment, hemoglobin levels treatment with ARCON had no significant effect on 5-year loco-regional control (LRC, 79% versus 75%; P = 0.44) and disease-free survival (DFS, 75% vs. 70%; P = 0.46) compared with accelerated radiotherapy. However, in patients with low pretreatment, hemoglobin levels ARCON significantly improved 5-year LRC (79% vs. 53%; P = 0.03) and DFS (68% vs. 45%; P = 0.04). In multivariate analysis including other prognostic factors, pretreatment hemoglobin remained prognostic for LRC and DFS in the accelerated radiotherapy treatment arm. No correlation between pretreatment hemoglobin levels and pimonidazole uptake was observed. CONCLUSION: Results from the randomized phase III trial support previous observations that ARCON has the potential to correct the poor outcome of cancer patients with anemia (ClinicalTrials.gov number, NCT00147732). Clin Cancer Res; 20(5); 1345-54. (c)2014 AACR

Geometry, thermodynamics, and finite-size corrections in the critical Potts model

We establish an intriguing connection between geometry and thermodynamics in the critical q-state Potts model on two-dimensional lattices, using the q-state bond-correlated percolation model (QBCPM) representation. We find that the number of clusters of the QBCPM has an energy-like singularity for q different from 1, which is reached and supported by exact results, numerical simulation, and scaling arguments. We also establish that the finite-size correction to the number of bonds, has no constant term and explains the divergence of related quantities as q --> 4, the multicritical point. Similar analyses are applicable to a variety of other systems.Comment: 12 pages, 6 figure

Structural and dynamical properties of superfluid helium: a density functional approach

We present a novel density functional for liquid 4He, properly accounting for the static response function and the phonon-roton dispersion in the uniform liquid. The functional is used to study both structural and dynamical properties of superfluid helium in various geometries. The equilibrium properties of the free surface, droplets and films at zero temperature are calculated. Our predictions agree closely to the results of ab initio Monte Carlo calculations, when available. The introduction of a phenomenological velocity dependent interaction, which accounts for backflow effects, is discussed. The spectrum of the elementary excitations of the free surface and films is studied.Comment: 37 pages, REVTeX 3.0, figures on request at [email protected]

N-body simulations of gravitational dynamics

We describe the astrophysical and numerical basis of N-body simulations, both of collisional stellar systems (dense star clusters and galactic centres) and collisionless stellar dynamics (galaxies and large-scale structure). We explain and discuss the state-of-the-art algorithms used for these quite different regimes, attempt to give a fair critique, and point out possible directions of future improvement and development. We briefly touch upon the history of N-body simulations and their most important results.Comment: invited review (28 pages), to appear in European Physics Journal Plu

Quantum Rotation of HCN and DCN in Helium-4

We present calculations of rotational absorption spectra of the molecules HCN and DCN in superfluid helium-4, using a combination of the Diffusion Monte Carlo method for ground state properties and an analytic many-body method (Correlated Basis Function theory) for the excited states. Our results agree with the experimentally determined effective moment of inertia which has been obtained from the $J=0\to 1$ spectral transition. The correlated basis function analysis shows that, unlike heavy rotors such as OCS, the J=2 and higher rotational excitations of HCN and DCN have high enough energy to strongly couple to rotons, leading to large shifts of the lines and accordingly to anomalous large spectroscopic distortion constants, to the emergence of roton-maxon bands, and to secondary peaks in the absorption spectra for J=2 and J=3.Comment: accepted by Phys. Rev. B; changes: included referee suggestions, removed typos, added 10 ref

Relaxation channels of two-vibron bound states in \alpha-helix proteins

Relaxation channels for two-vibron bound states in an anharmonic alpha-helix protein are studied. It is pointed out that the relaxation originates in the interaction between the dressed anharmonic vibrons and the remaining phonons. This interaction is responsible for the occurrence of transitions between two-vibron eigenstates mediated by both phonon absorption and phonon emission. At biological temperature, it is shown that the relaxation rate does not significantly depends on the nature of the two-vibron state involved in the process. Therefore, the lifetime for both bound and free states is of the same order of magnitude and ranges between 0.1 and 1.0 ps for realistic parameters. By contrast, the relaxation channels strongly depend on the nature of the two-vibron states which is a consequence of the breather-like behavior of the two-vibron bound states.Comment: octobre 2003 - soumis Phys. Rev.