2,491 research outputs found
Cell Death and Disease: a new journal for a central area of pathophysiology
If pathophysiology were a fan propeller, cell death would constitute the pivot. Indeed, most diseases are connected to deregulated cell death in some way. Excessive, unwarranted cell death accounts for pathological cell loss, be it slowly degenerative as in Alzheimer's disease or dramatically acute as in stroke and myocardial infarction. Infectious pathogens manipulate cell death pathways to induce or inhibit the death of host cells at will and to subvert the immune recognition of ‘dangerous’ cell death. Finally, cancer is inexorably linked to a partial suppression of cell death programs in tumor cells, although therapy aims to (re)activate such lethal programs. Cell Death and Disease, a new open-access, online journal aims to provide center stage to fundamental, disease-oriented and translational research in cell death. [Opening paragraph
Universality of the Gunn effect: self-sustained oscillations mediated by solitary waves
The Gunn effect consists of time-periodic oscillations of the current flowing
through an external purely resistive circuit mediated by solitary wave dynamics
of the electric field on an attached appropriate semiconductor. By means of a
new asymptotic analysis, it is argued that Gunn-like behavior occurs in
specific classes of model equations. As an illustration, an example related to
the constrained Cahn-Allen equation is analyzed.Comment: 4 pages,3 Post-Script figure
Two-electron atoms, ions and molecules
The quantum mechanics of two-electron systems is reviewed, starting with the
ground state of the helium atom and helium-like ions, with central charge . For Z=1, demonstrating the stability of the negative hydrogen ion, H,
cannot be achieved using a mere product of individual electron wave functions,
and requires instead an explicit account for the anticorrelation among the two
electrons. The wave function proposed by Chandrasekhar is revisited, where the
permutation symmetry is first broken and then restored by a counter-term. More
delicate problems can be studied using the same strategy: the stability of
hydrogen-like ions for any value of the proton-to-electron mass
ratio ; the energy of the lowest spin-triplet state of helium and
helium-like ions; the stability of the doubly-excited hydrogen ion with
unnatural parity. The positronium molecule , which has been
predicted years ago and discovered recently, can also be shown to be stable
against spontaneous dissociation, though the calculation is a little more
involved. Emphasis is put on symmetry breaking which can either spoil or
improve the stability of systems.Comment: 16 pages, 2 figure
The use of mobile phones for skin tumor screening
A lot of importance is attributed to mobile telemedicine these days, a topic that encompasses a wide and ever growing range of applications. Small, handheld devices such as camera mobile phones have come into every day use providing technically sophisticated tasks on a user-friendly level and can therefore be easily used in various fields of telemedicine. Dermatology is a perfect candidate for the use of telemedicine tools in general, as well as mobile devices in particular. The unique aspect of mobile teledermatology is that this system represents a filtering, or triage system, allowing a sensitive approach for the management of patients with emergent skin diseases. In order to investigate the feasibility of teleconsultation using a new generation of cellular phones, a clinical study to evaluate the accuracy of online diagnosis of skin tumours was conducted. Teledermoscopy represents a recent development of teledermatology that might add up additional information in the diagnosis of pigmented skin lesions. Teledermatology, mobile as well as stationary, can advance the reliability of diagnosis by expert consultations without expensive and time-consuming relocations. Consequently, the quality of patient's care can be raised and the costs of the health care system can be reduced
Stationary states and phase diagram for a model of the Gunn effect under realistic boundary conditions
A general formulation of boundary conditions for semiconductor-metal contacts
follows from a phenomenological procedure sketched here. The resulting boundary
conditions, which incorporate only physically well-defined parameters, are used
to study the classical unipolar drift-diffusion model for the Gunn effect. The
analysis of its stationary solutions reveals the presence of bistability and
hysteresis for a certain range of contact parameters. Several types of Gunn
effect are predicted to occur in the model, when no stable stationary solution
exists, depending on the value of the parameters of the injecting contact
appearing in the boundary condition. In this way, the critical role played by
contacts in the Gunn effect is clearly stablished.Comment: 10 pages, 6 Post-Script figure
Constraints on transmission, dispersion, and density of states in dielectric multilayers and stepwise potential barriers with arbitrary layer arrangement
Normal-incidence transmission and dispersion properties of optical
multilayers and one-dimensional stepwise potential barriers in the
non-tunneling regime are analytically investigated. The optical paths of every
constituent layer in a multilayer structure, as well as the parameters of every
step of the stepwise potential barrier, are constrained by a generalized
quarter-wave condition. No other restrictions on the structure geometry is
imposed, i.e., the layers are arranged arbitrarily. We show that the density of
states (DOS) spectra of the multilayer or barrier in question are subject to
integral conservation rules similar to the Barnett-Loudon sum rule but ocurring
within a finite frequency or energy interval. In the optical case, these
frequency intervals are regular. For the potential barriers, only non-periodic
energy intervals can be present in the spectrum of any given structure, and
only if the parameters of constituent potential steps are properly chosen.
Abstract The integral conservation relations derived analytically have also
been verified numerically. The relations can be used in dispersion-engineered
multilayer-based devices, e.g., ultrashort pulse compressors or ultracompact
optical delay lines, as well as to design multiple-quantum-well electronic
heterostructures with engineered DOS.Comment: 10 pages, 5 figures, to be submitted to PR
Absorption and wavepackets in optically excited semiconductor superlattices driven by dc-ac fields
Within the one-dimensional tight-binding minibands and on-site
Coloumbic interaction approximation, the absorption spectrum and coherent
wavepacket time evolution in an optically excited semiconductor superlattice
driven by dc-ac electric fields are investigated using the semiconductor Bloch
equations.
The dominating roles of the ratios of dc-Stark to external ac frequency, as
well as ac-Stark to external ac frequency, is emphasized. If the former is an
integer , then also harmonics are present within one Stark
frequency, while the fractional case leads to the formation of excitonic
fractional ladders. The later ratio determines the size and profile of the
wavepacket. In the absence of excitonic interaction it controls the maximum
size wavepackets reach within one cycle, while the interaction produces a
strong anisotropy and tends to palliate the dynamic wavepacket localization.Comment: 14 pages, 7 postscript figure
Bim and Bmf synergize to induce apoptosis in Neisseria gonorrhoeae infection
Abstract: Bcl-2 family proteins including the pro-apoptotic BH3-only proteins are central regulators of apoptotic cell death. Here we show by a focused siRNA miniscreen that the synergistic action of the BH3-only proteins Bim and Bmf is required for apoptosis induced by infection with Neisseria gonorrhoeae (Ngo). While Bim and Bmf were associated with the cytoskeleton of healthy cells, they both were released upon Ngo infection. Loss of Bim and Bmf from the cytoskeleton fraction required the activation of Jun-N-terminal kinase-1 (JNK-1), which in turn depended on Rac-1. Depletion and inhibition of Rac-1, JNK-1, Bim, or Bmf prevented the activation of Bak and Bax and the subsequent activation of caspases. Apoptosis could be reconstituted in Bim-depleted and Bmf-depleted cells by additional silencing of antiapoptotic Mcl-1 and Bcl-XL, respectively. Our data indicate a synergistic role for both cytoskeletal-associated BH3-only proteins, Bim, and Bmf, in an apoptotic pathway leading to the clearance of Ngo-infected cells. Author Summary: A variety of physiological death signals, as well as pathological insults, trigger apoptosis, a genetically programmed form of cell death. Pathogens often induce host cell apoptosis to establish a successful infection. Neisseria gonorrhoeae (Ngo), the etiological agent of the sexually transmitted disease gonorrhoea, is a highly adapted obligate human-specific pathogen and has been shown to induce apoptosis in infected cells. Here we unveil the molecular mechanisms leading to apoptosis of infected cells. We show that Ngo-mediated apoptosis requires a special subset of proapoptotic proteins from the group of BH3-only proteins. BH3-only proteins act as stress sensors to translate toxic environmental signals to the initiation of apoptosis. In a siRNA-based miniscreen, we found Bim and Bmf, BH3-only proteins associated with the cytoskeleton, necessary to induce host cell apoptosis upon infection. Bim and Bmf inactivated different inhibitors of apoptosis and thereby induced cell death in response to infection. Our data unveil a novel pathway of infection-induced apoptosis that enhances our understanding of the mechanism by which BH3-only proteins control apoptotic cell death
Terahertz superlattice parametric oscillator
We report a GaAs/AlAs superlattice parametric oscillator. It was pumped by a
microwave field (power few mW) and produced 3rd harmonic radiation (frequency
near 300 GHz). The nonlinearity of the active superlattice was due to Bragg
reflections of conduction electrons at the superlattice planes. A theory of the
nonlinearity indicates that parametric oscillation should be possible up to
frequencies above 10 THz. The active superlattice may be the object of further
studies of predicted extraordinary nonlinearities for THz fields.Comment: 10 pages, 4 figure
- …