Observation of Fe-H/D modes by nuclear resonant vibrational spectroscopy

Metal-hydrogen bonding is important in chemistry and catalysis, but H atoms are often difficult to observe, especially in metalloproteins. In this work we show that Fe-H interactions can be probed by nuclear resonance vibrational spectroscopy at the 14.4 keV 57Fe nuclear resonance. An important advantage of this method, compared to Raman and IR spectroscopy, is the selectivity for modes that involve 57Fe motion. We present data on the FeS4 site in rubredoxin and the [FeH(D)6]2- ion. Prospects for studying more complex systems are discussed.     

Value iteration in countable state average cost Markov decision processes with unbounded costs

We deal with countable state Markov decision processes with finite action sets and (possibly) unbounded costs. Assuming the existence of an expected average cost optimal stationary policyf, with expected average costg, when canf andg be found using undiscounted value iteration? We give assumptions guaranteeing the convergence of a quantity related tong?Ν _n (i), whereΝ _n (i) is the minimum expectedn-stage cost when the process starts in statei. The theory is applied to a queueing system with variable service rates and to a queueing system with variable arrival parameter.     

Thermal energy transport in harmonic systems

One and two-dimensional oscillator systems are constructed so that individual oscillators are bound to their home positions and coupled to nearest neighbors by linear forces; both systems are treated for the case of weak coupling. The two-dimensional system has a tensor binding force that does not permit it to be decoupled into two noninteracting systems.Segments and strips are treated as thermodynamic systems in contact with a heat bath and Gaussian initial probability densities are used to compute correlations. Expressions for entropy and “temperature” are computed by relating initial system and bath variances to equilibrium temperature.Asymptotic relations for “temperature” are found that show the degree of coupling between dimensions affects the rate of approach to equilibrium, but only through the coefficient of time and not its power. Both systems approach equilibrium as t^?1 rather than $\text{t}{}^{\mathrm{<mtext>?</mtext><mtext>1</mtext><mtext>2</mtext>}}$ as predicted by continuum theory.     

Small‐Band‐Gap Halide Double Perovskites

Despite their compositional versatility, most halide double perovskites feature large band gaps. Herein, we describe a strategy for achieving small band gaps in this family of materials. The new double perovskites Cs₂AgTlX₆ (X=Cl ( 1 ) and Br ( 2 )) have direct band gaps of 2.0 and 0.95 eV, respectively, which are approximately 1 eV lower than those of analogous perovskites. To our knowledge, compound 2 displays the lowest band gap for any known halide perovskite. Unlike in A^IB^IIX₃ perovskites, the band‐gap transition in A^I₂BB′X₆ double perovskites can show substantial metal‐to‐metal charge‐transfer character. This band‐edge orbital composition is used to achieve small band gaps through the selection of energetically aligned B‐ and B′‐site metal frontier orbitals. Calculations reveal a shallow, symmetry‐forbidden region at the band edges for 1 , which results in long (μs) microwave conductivity lifetimes. We further describe a facile self‐doping reaction in 2 through Br₂ loss at ambient conditions.     

THE EVOLUTION OF PHOTODYNAMIC THERAPY TECHNIQUES IN THE TREATMENT OF INTRAOCULAR TUMORS

Abstract The techniques of photodynamic therapy (PDT) and the indications for its use in the treatment of intraocular tumors have evolved during the years in which it has been assessed in patients at our institution. It is now clear that transcorneal PDT delivered at a subthermal dose-rate to the surface of a pigmented lesion such as choroidal melanoma has little effect. In the absence of pigment, however, as in the case of retinoblastoma or amelanotic melanoma of the iris or choroid, the tumor kill attributed to PDT alone is significant. Data from animal tumor models in our institution and from patient studies elsewhere suggest that the addition of heat with the light delivery will predictably improve the outcome of the treatment of pigmented lesions. Ocular PDT delivered in conjunction with heat will be useful clinically as an adjunct to scleral plaque therapy by reducing the height of a lesion and concurrently the dose of radiation necessary at the base of the tumor for sterilization. Since the clinical tumoricidal effect of PDT is now known to be due at least in part to vascular damage, trans-scleral application of light to the base of melanomas and occlusion of its blood supply holds significant promise of efficacy with continued improvement of the light delivery system. Finally, a transpupillary approach to occlusion of the choroidal vascular supply to a melanoma by surrounding the tumor with photodynamic lesions may provide the best approach for ocular PDT as a primary therapy.     

Magnetic field dependence of electron spin polarization generated through radical-triplet interactions

The magnetic field dependence of electron spin polarization (ESP), generated in free radicals when they encounter photoexcited triplets, was measured experimentally and analyzed theoretically. The time-resolved electron paramagnetic resonance measurements were performed with a microwave setup consisting of low-loss dielectric ring resonators with tunable microwave frequencies and the corresponding magnetic fields. The ESP of the radical was found in the magnetic field range of 170-370 mT, and the results of the calculation based on the numerical solution of the stochastic Liouville equation were found to be in line with the experimental data showing that ESP decreases when the magnetic field increases.     

THE INFLUENCE OF SODIUM PENTOBARBITAL ANESTHESIA ON in vivo PHOTODYNAMIC THERAPY

Abstract The use of sodium pentobarbital anesthesia 50 jig gm⁻¹ during localized photodynamic therapy (PDT) was examined in C57BL/6 mice transplanted with the pigmented B-16 melanoma. A 10 mg kg⁻¹ i.p. injection of Photofrin II was administered 24 h prior to light exposure (630 nm, 150 mW, cm⁻², 300-500 J cm⁻²). Separate groups of mice were utilized to monitor tumour temperature and PDT tumor response. Core tumor temperatures decreased by approx. 10^oC following sodium pentobarbital administration. Tumor responses were determined by documenting the percentage of treated animals without tumor recurrences for a period of 50 days following PDT. Superior PDT induced tumor responses were obtained in control (non-anesthetized) mice following light doses of 400 and 500 J cm⁻². The results of this study indicate that sodium pentobarbital can induce a protective effect on B-16 melanomas treated with PDT.