States prepared by decay

We consider the time evolution of a discrete state embedded in a continuum. Results from scattering theory can be utilized to solve the initial value problem and discuss the system as a model of wave packet preparation. Extensive use is made of the analytic properties of the propagators, and simple model systems are evaluated to illustrate the argument. We verify the exponential appearence of the continuum state and its propagation as a localized wave packet.Comment: 22 pages, Latex2.09, 6 Postscript figures embedded using psfig, see also http://www.physics.helsinki.fi/~kasuomin/ To appear in a Special Issue of Journal of Modern Optics (1997

Spin relaxation of localized electrons in n-type semiconductors

The mechanisms that determine spin relaxation times of localized electrons in impurity bands of n-type semiconductors are considered theoretically and compared with available experimental data. The relaxation time of the non-equilibrium angular momentum is shown to be limited either by hyperfine interaction, or by spin-orbit interaction in course of exchange-induced spin diffusion. The energy relaxation time in the spin system is governed by phonon-assisted hops within pairs of donors with an optimal distance of about 4 Bohr radii. The spin correlation time of the donor-bound electron is determined either by exchange interaction with other localized electrons, or by spin-flip scattering of free conduction-band electrons. A possibility of optical cooling of the spin system of localized electrons is discussed.Comment: Submitted to the special issue "Optical Orientation", Semiconductor Science and Technolog

Malarial Hemozoin Is a Nalp3 Inflammasome Activating Danger Signal

BACKGROUND: Characteristic symptoms of malaria include recurrent fever attacks and neurodegeneration, signs that are also found in patients with a hyperactive Nalp3 inflammasome. Plasmodium species produce a crystal called hemozoin that is generated by detoxification of heme after hemoglobin degradation in infected red blood cells. Thus, we hypothesized that hemozoin could activate the Nalp3 inflammasome, due to its particulate nature reminiscent of other inflammasome-activating agents. METHODOLOGY/PRINCIPAL FINDINGS: We found that hemozoin acts as a proinflammatory danger signal that activates the Nalp3 inflammasome, causing the release of IL-1beta. Similar to other Nalp3-activating particles, hemozoin activity is blocked by inhibiting phagocytosis, K(+) efflux and NADPH oxidase. In vivo, intraperitoneal injection of hemozoin results in acute peritonitis, which is impaired in Nalp3-, caspase-1- and IL-1R-deficient mice. Likewise, the pathogenesis of cerebral malaria is dampened in Nalp3-deficient mice infected with Plasmodium berghei sporozoites, while parasitemia remains unchanged. SIGNIFICANCE/CONCLUSIONS: The potent pro-inflammatory effect of hemozoin through inflammasome activation may possibly be implicated in plasmodium-associated pathologies such as cerebral malaria

Malarial Hemozoin Is a Nalp3 Inflammasome Activating Danger Signal

BACKGROUND: Characteristic symptoms of malaria include recurrent fever attacks and neurodegeneration, signs that are also found in patients with a hyperactive Nalp3 inflammasome. Plasmodium species produce a crystal called hemozoin that is generated by detoxification of heme after hemoglobin degradation in infected red blood cells. Thus, we hypothesized that hemozoin could activate the Nalp3 inflammasome, due to its particulate nature reminiscent of other inflammasome-activating agents. METHODOLOGY/PRINCIPAL FINDINGS: We found that hemozoin acts as a proinflammatory danger signal that activates the Nalp3 inflammasome, causing the release of IL-1beta. Similar to other Nalp3-activating particles, hemozoin activity is blocked by inhibiting phagocytosis, K(+) efflux and NADPH oxidase. In vivo, intraperitoneal injection of hemozoin results in acute peritonitis, which is impaired in Nalp3-, caspase-1- and IL-1R-deficient mice. Likewise, the pathogenesis of cerebral malaria is dampened in Nalp3-deficient mice infected with Plasmodium berghei sporozoites, while parasitemia remains unchanged. SIGNIFICANCE/CONCLUSIONS: The potent pro-inflammatory effect of hemozoin through inflammasome activation may possibly be implicated in plasmodium-associated pathologies such as cerebral malaria

Herringbone ordering and lattice distortions in a planar-molecule model for Langmuir monolayers

A model of planar molecules, made up of "atoms" interacting by Lennard-Jones potentials and arranged to mimic the cross section of alkyl chains, is used to study the problem of backbone plane ordering in Langmuir monolayers. It is shown that two minima of the interaction energy are reached if molecules lie on the sites of a centered rectangular lattice in a herringbone configuration with two different dihedral angles. These orientationally ordered phases can be related to the so-called herringbone and pseudoherringbone structures, whose lattice distortions qualitatively agree with those determined by means of grazing incidence x-ray diffraction experiments on Langmuir monolayers. A third energy minimum is obtained for a configuration of parallel molecules on an oblique lattice, which has also been observed in some experiments. The competition between the three phases is investigated, upon varying geometric parameters of the model molecules and surface pressure. The effect of temperature is analyzed in a mean field approximation, by taking into account the orientational entropy contribution on a lattice system with variable unit cell parameters. In this framework the transition to an orientationally disordered phase is also pointed out

Lanthanoid “Bottlebrush” Clusters: Remarkably Elongated Metal-Oxo Core Structures with Controllable Lengths

Large metal-oxo clusters consistently assume spherical or regular polyhedral morphologies rather than high-aspect-ratio structures. Access to elongated core structures has now been achieved by the reaction of lanthanoid salts with a tetrazole-functionalized calixarene in the presence of a simple carboxylate coligand.The resulting Ln19 and Ln12 clusters are constructed from apex-fused Ln5O6 trigonal bipyramids and are formed consistently under a range of reaction conditions and reagent ratios. Altering the carboxylate coligandstructure reliably controls the cluster length, giving access to a new class of rod-like clusters of variable length

Self-Association of Organic Solutes in Solution: A NEXAFS Study of Aqueous Imidazole

N K-edge near-edge X-ray absorption fine-structure (NEXAFS) spectra of imidazole in concentrated aqueous solutions have been acquired. The NEXAFS spectra of the solution species differ significantly from those of imidazole monomers in the gas phase and in the solid state of imidazole, demonstrating the strong sensitivity of NEXAFS to the local chemical and structural environment. In a concentration range from 0.5 to 8.2 mol L−1 the NEXAFS spectrum of aqueous imidazole does not change strongly, confirming previous suggestions that imidazole self-associates are already present at concentrations more dilute than the range investigated here. We show that various types of electronic structure calculations (Gaussian, StoBe, CASTEP) provide a consistent and complete interpretation of all features in the gas phase and solid state spectra based on ground state electronic structure. This suggests that such computational modelling of experimental NEXAFS will permit an incisive analysis of the molecular interactions of organic solutes in solutions. It is confirmed that microhydrated clusters with a single imidazole molecule are poor models of imidazole in aqueous solution. Our analysis indicates that models including both a hydrogen-bonded network of hydrate molecules, and imidazole–imidazole interactions, are necessary to explain the electronic structure evident in the NEXAFS spectra

Evaluation of a novel magneto-optical method for the detection of malaria parasites

Improving the efficiency of malaria diagnosis is one of the main goals of current malaria research. We have recently developed a magneto-optical (MO) method which allows high-sensitivity detection of malaria pigment (hemozoin crystals) in blood via the magnetically induced rotational motion of the hemozoin crystals. Here, we evaluate this MO technique for the detection of Plasmodium falciparum in infected erythrocytes using in-vitro parasite cultures covering the entire intraerythrocytic life cycle. Our novel method detected parasite densities as low as approximately 40 parasites per microliter of blood (0.0008% parasitemia) at the ring stage and less than 10 parasites/microL (0.0002% parasitemia) in the case of the later stages. These limits of detection, corresponding to approximately 20 pg/microL of hemozoin produced by the parasites, exceed that of rapid diagnostic tests and compete with the threshold achievable by light microscopic observation of blood smears. The MO diagnosis requires no special training of the operator or specific reagents for parasite detection, except for an inexpensive lysis solution to release intracellular hemozoin. The devices can be designed to a portable format for clinical and in-field tests. Besides testing its diagnostic performance, we also applied the MO technique to investigate the change in hemozoin concentration during parasite maturation. Our preliminary data indicate that this method may offer an efficient tool to determine the amount of hemozoin produced by the different parasite stages in synchronized cultures. Hence, it could eventually be used for testing the susceptibility of parasites to antimalarial drugs

A supramolecular helix that disregards chirality

The functions of complex crystalline systems derived from supramolecular biological and non-biological assemblies typically emerge from homochiral programmed primary structures via first principles involving secondary, tertiary and quaternary structures. In contrast, heterochiral and racemic compounds yield disordered crystals, amorphous solids or liquids. Here, we report the self-assembly of perylene bisimide derivatives in a supramolecular helix that in turn self-organizes in columnar hexagonal crystalline domains regardless of the enantiomeric purity of the perylene bisimide. We show that both homochiral and racemic perylene bisimide compounds, including a mixture of 21 diastereomers that cannot be deracemized at the molecular level, self-organize to form single-handed helical assemblies with identical single-crystal-like order. We propose that this high crystalline order is generated via a cogwheel mechanism that disregards the chirality of the self-assembling building blocks. We anticipate that this mechanism will facilitate access to previously inaccessible complex crystalline systems from racemic and homochiral building blocks