An electrically controlled holographic switch is proposed as a building block for a free-space optical interconnection network. The switch is based on the voltage-controlled photorefractive effect in KLTN crystals at the paraelectric phase. It is built of electrically controlled Bragg gratings stored in the volume of the crystal. A compact switch that connects four high-speed fiber-optic communication channels with high efficiency is demonstrated experimentally. The switch performance is investigated and optimized. This switch is extremely attractive for cascaded switching arrays such as those found in multistage interconnect networks.
We present a theoretical analysis of the phase behavior of solutions containing DNA, cationic lipids, and nonionic (helper) lipids. Our model allows for five possible structures, treated as incompressible macroscopic phases: two lipid-DNA composite (lipoplex) phases, namely, the lamellar (L-alpha(C)) and hexagonal (H-II(C)) complexes; two binary (cationic/neutral) lipid phases, that is, the bilayer (L-alpha) and inverse-hexagonal (H-II) structures, and uncomplexed DNA. The free energy of the four lipid-containing phases is expressed as a sum of composition-dependent electrostatic, elastic, and mixing terms. The electrostatic free energies of all phases are calculated based on Poisson-Boltzmann theory. The phase diagram of the system is evaluated by minimizing the total free energy of the three-component mixture with respect to all the compositional degrees of freedom. We show that the phase behavior, in particular the preferred lipid-DNA complex geometry, is governed by a subtle interplay between the electrostatic, elastic, and mixing terms, which depend, in turn, on the lipid composition and lipid/DNA ratio. Detailed calculations are presented for three prototypical systems, exhibiting markedly different phase behaviors. The simplest mixture corresponds to a rigid planar membrane as the lipid source, in which case, only lamellar complexes appear in solution. When the membranes are ``soft'' (i.e., low bending modulus) the system exhibits the formation of both lamellar and hexagonal complexes, sometimes coexisting with each other, and with pure lipid or DNA phases. The last system corresponds to a lipid mixture involving helper lipids with strong propensity toward the inverse-hexagonal phase. Here, again, the phase diagram is rather complex, revealing a multitude of phase transitions and coexistences. Lamellar and hexagonal complexes appear, sometimes together, in different regions of the phase diagram.
Photodissociation and recombination of an F-2 molecule embedded in an Ar cluster is investigated. The electronic states involved are described by the valence bond approach for the F(P-2)+F(P-2) interaction, with spin-orbit coupling included and the anisotropic interactions between F and Ar atoms described by the diatomics-in-molecules (DIM) approach. The potential energy surfaces for 36 electronic states and the nonadiabatic couplings between them are constructed in this basis. The surface hopping method is used for dynamical simulations. The main results are: (i) Spin nonconserving transitions play a crucial role both in the dissociation and in the recombination dynamics. (ii) The ratio between the population of the triplet states and the population of the singlet states reaches the statistical equilibrium value of 3:1 60 fs after the photoexcitation, but the population of specific singlet and triplet states remains nonstatistical for at least 1.5 ps. (iii) Recombination on the only bound excited state ((3)Pi (u)) becomes significant within 100 fs and builds up to 40% of the trajectories within 1 ps after excitation of the cluster with 4.6 eV. This is in accord with recent experiments on ClF/Ar solid, where strong emission from this state was found. (iv) 3% of recombination on the ground (1)Sigma (g) state is found as well. (v) For excitation energy of 4.6 eV, the dissociation can be direct or delayed. In delayed dissociation the F photofragments hit the Ar cage more than once before escaping the cage. (vi) For excitation energy of 6.53 eV the yield of dissociation was found to be 100%, and the dissociation is direct only. (C) 2000 American Institute of Physics. [S0021-9606(00)01240-X].
Ultraviolet (UV) photodissociation experiments are carried out for Ar-n(HBr) clusters in which the HBr is adsorbed on the surface of the Ar-n, and also on isomers of these systems in which HBr is embedded within the rare-gas cluster. The mean size of the cluster distribution in the experiments is around (n) over bar=130. The kinetic energy distribution (KED) of the hydrogen atoms that left the clusters is measured. Molecular dynamics (MD) simulations of the photodissociation of the chemically similar clusters Ar-n(HCl) are used to provide a qualitative interpretation of the experimental results. The clusters with embedded HBr give a very cold H-atom KED. The clusters with the surface-adsorbed HBr give a KED with two peaks, one corresponding to very low energy H atoms and the other pertaining to high energies, of the order of 1.35 eV. The theoretical simulations show that already for n=54, there is a strong cage effect for the ``embedded'' molecule case, resulting in slow H atoms. The surface-adsorbed case is interpreted as due to two types of possible adsorption sites of HX on Ar-55: for a locally smooth adsorption site, the cage effect is relatively weak, and hot H atoms emerge. Sites where the HBr is adsorbed at a vacancy of Ar-n lead to ``encapsulation'' of the H atom produced, with a strong cage effect. A weak tail of H atoms with energies well above the HBr monomer excess energy is observed for the embedded case. Simulations support that this is due to a second photon absorption by recombined, but still vibrationally hot, HBr. The results throw light on the differences between the cage effect inside bulk structure and at surfaces. (C) 2000 American Institute of Physics. [S0021-9606(00)00925-9].
A blue–red reversible optical switch has been created by combining EuIII, pyridine, and a fluorescent organic chromophore. The initial solution exhibits the expected blue emission of the chromophore until UV irradiation leads to red emission (see Figure), a process that is ascribed to protonation of the pyridine and formation of a charge-transfer complex with the chromophore in the excited state, allowing the red EuIII photoluminescence to be emitted.
In the present work we show a way of controlling photoluminescence (PL) properties through photoinduced quasi-crystal formation in a system based on poly(4-vinyl pyridine) (P4VPy). Under UV irradiation at 380 nm, concentrated solutions of P4VPy in pyridine turn into gel. This phase transition results in changes in the optical properties of this polymer. The position of the PL maximum can be changed continuously from 440 to 480 nm during irradiation. After several minutes of UV irradiation a new red-shifted PL at 492 nm appears upon excitation by light of a wavelength corresponding to that of the initial PL maximum, which is also red-shifted during irradiation. Solutions of P4VPy in pyrimidine show similar behavior, but those in pyridazine do not exhibit such behavior. We have found that the reason for the observed changes in the electronic properties is a photoinduced directional ordering of polymer molecules in a special quasi-crystal formation. The process originates from a structural change in the side chain of P4VPy, namely, protonation of the polymeric pyridine after solvation. During irradiation, the polymeric pyridinium ion interacts with neutral polymeric pyridine molecules. Interchain interaction through hydrogen bonds lead to an electronic property change. We observed that the process of photoinduced sol-gel transformation is reversible. Mechanical perturbation or heating can convert the gel back to a fluid solution. The red-shifted PL is not observed, and the initial PL is blue-shifted to 450 nm and stays there.
OBJECTIVES:
We sought to determine whether early prophylaxis with an L -type calcium channel blocker reduces the incidence and morbidity associated with atrial fibrillation/flutter and supraventricular tachyarrhythmia after major thoracic operations.
METHODS:
In this randomized, double-blind, placebo-controlled study, 330 patients were given either intravenous diltiazem (n = 167) or placebo (n = 163) immediately after lobectomy (> or =60 years) or pneumonectomy (> or =18 years) and orally thereafter for 14 days. The primary end point with respect to efficacy was a sustained (> or =15 minutes) or clinically significant atrial arrhythmia during treatment.
RESULTS:
Postoperative atrial arrhythmias (atrial fibrillation/flutter = 60; supraventricular tachyarrhythmias = 5) occurred in 25 (15%) of the 167 patients in the diltiazem group and 40 (25%) of the 163 patients in the placebo group (P = .03). When compared with placebo, diltiazem nearly halved the incidence of clinically significant arrhythmias (17/167 [10%] vs. 31/163 [19%], P = .02). The 2 groups did not differ in the incidence of other major postoperative complications or overall duration or costs of hospitalization. No serious adverse effects caused by diltiazem were seen.
CONCLUSIONS:
After major thoracic operations, prophylactic diltiazem reduced the incidence of clinically significant atrial arrhythmias in patients considered at high risk for this complication.
Lay summary:
What drives successful IT projects in the public sector? The article examines the leadership skills necessary to implement such projects. Surprisingly, the article suggests that technical and administrative skills are not the most important. Instead, the ability to navigate organizational politics is critical. Leaders with political skill tailor IT projects to fit the reality of their organization; leaders with primarily technical skill tend to rely on less successful generic solutions.
Publication significance:
Public sector IT projects often suffer from poor implementation, failing to meet their budget and time-schedule. This article enriches our understanding of the leadership skills necessary to ensure successful project implementation. It finds that technical and administrative skills must be accompanied by political skill. This finding has significant practical implications for public organizations and also broadens the scope of scholarly research on organizational leadership.
The invention provides a sustained release, polymer-based, water insol. bead, comprising a polymeric matrix contg. a plurality of emulsion droplets, the droplets being formed from at least one surface-active mol., at least one volatile hydrophobic component and water, wherein the volatile component is released from the water-insol. bead in atm. air. The volatile components are insect pheromones or essential oils. [on SciFinder(R)]
OBJECTIVE:
To determine whether greater changes in plasma endothelin-1 (ET-1) concentrations and right ventricular systolic pressure occur after major thoracic surgery than after major abdominal operations.
DESIGN:
Prospective study.
SETTING:
University hospital.
PARTICIPANTS:
Patients undergoing elective thoracotomies (n = 12) or laparotomies (n = 10).
INTERVENTIONS:
ET-1 was measured from blood obtained before anesthesia and again on postoperative days 1, 2, 3, and 5 (or 6). Transthoracic echocardiography was performed before surgery and on postoperative day 2 to evaluate right-sided heart function.
MEASUREMENTS AND MAIN RESULTS:
After abdominal and thoracic surgery, systemic and estimated pulmonary vascular pressures were normal in both groups and unaffected by surgery. Plasma ET-1 concentrations decreased from baseline values during the first postoperative week with no differences between the groups.
CONCLUSIONS:
In patients without organic heart disease, plasma ET-1 levels do not increase in response to major abdominal or thoracic surgery. Whether or not plasma ET-1 concentrations are elevated in patients developing clinically significant postoperative pulmonary hypertension requires further study.
Compns. and methods useful for the in vivo delivery of water-insol. drugs (e.g., anticancer paclitaxel) in which the drug agent is delivered in the form of suspended particles coated with protein (which acts as a stabilizer) are described. In particular, protein and the drug in a biocompatible dispersing medium are subjected to high shear, in the absence of any conventional surfactants, and also in the absence of any polymeric core material for the particles. The procedure yields particles with a diam. of <1 μ. The use of specific compn. and prepn. conditions (e.g., addn. of a polar solvent to the org. phase), and careful election of the proper org. phase and phase fraction, enables the reproducible prodn. of unusually small nanoparticles of less than 200 nm diam., which can be sterile-filtered. The particulate system produced can be converted into a redispersible dry powder comprising nanoparticles of water-insol. drug coated with a protein, and free protein to which mols. of the drug are bound. This results in a unique delivery system, in which part of the drug is readily bioavailable (in the form of mols. bound to the protein), and part of the drug is present within particles without any polymeric matrix. Thus, 20 mg paclitaxel is dissolved in 1.0 mL methylene chloride and the soln. mixed with 4.0 mL human serum albumin soln. The mixt. was homogenized in order to form a crude emulsion and then sonicated. The dispersion was further lyophilized for 48 h without adding any cryoprotectant. The particle size after reconstitution was the same as before lyophilization. [on SciFinder(R)]
The feedback mode of the scanning electrochem. microscope (SECM) was used to induce and measure charge-transfer coupling (CTC) between two ion-transfer (IT) processes across liq./liq. interfaces. Results are interpreted using a general model for coupling processes under steady-state conditions that is also applicable to other modes of coupling such as IT-ET and ET-ET (ET = electron transfer). The measured feedback curves demonstrate the effect of mass-transfer limitations in these processes on the potential across the interface, shedding new light on the dynamics of bioenergetics and phase-transfer catalysis systems as well as on previous SECM studies of liq./liq. interfaces. [on SciFinder(R)]
We study two-person repeated games in which a player with a restricted set of strategies plays against an unrestricted player. An exogenously given bound on the complexity of strategies, which is measured by the size of the smallest automata that implement them, gives rise to a restriction on strategies available to a player. We examine the asymptotic behavior of the set of equilibrium payoffs as the bound on the strategic complexity of the restricted player tends to infinity, but sufficiently slowly. Results from the study of zero sum case provide the individually rational payoff levels.
We investigate the asymptotic behavior of the maxmin values of repeated two-person zero-sum games with a bound on the strategic entropy of the maximizer's strategies while the other player is unrestricted. We will show that if the bound (n), a function of the number of repetitions n, satisfies the condition (n)/n (n), then the maxmin value Wn ((n)) converges to (cavU)(), the concavification of the maxmin value of the stage game in which the maximizer's actions are restricted to those with entropy at most . A similar result is obtained for the infinitely repeated games.
