2,659 research outputs found
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
Axisymmetric pulse recycling and motion in bulk semiconductors
The Kroemer model for the Gunn effect in a circular geometry (Corbino disks)
has been numerically solved. The results have been interpreted by means of
asymptotic calculations. Above a certain onset dc voltage bias, axisymmetric
pulses of the electric field are periodically shed by an inner circular
cathode. These pulses decay as they move towards the outer anode, which they
may not reach. As a pulse advances, the external current increases continuously
until a new pulse is generated. Then the current abruptly decreases, in
agreement with existing experimental results. Depending on the bias, more
complex patterns with multiple pulse shedding are possible.Comment: 8 pages, 15 figure
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
Expression, Delivery and Function of Insecticidal Proteins Expressed by Recombinant Baculoviruses
Since the development of methods for inserting and expressing genes in baculoviruses, a line of research has focused on developing recombinant baculoviruses that express insecticidal peptides and proteins. These recombinant viruses have been engineered with the goal of improving their pesticidal potential by shortening the time required for infection to kill or incapacitate insect pests and reducing the quantity of crop damage as a consequence. A wide variety of neurotoxic peptides, proteins that regulate insect physiology, degradative enzymes, and other potentially insecticidal proteins have been evaluated for their capacity to reduce the survival time of baculovirus-infected lepidopteran host larvae. Researchers have investigated the factors involved in the efficient expression and delivery of baculovirus-encoded insecticidal peptides and proteins, with much effort dedicated to identifying ideal promoters for driving transcription and signal peptides that mediate secretion of the expressed target protein. Other factors, particularly translational efficiency of transcripts derived from recombinant insecticidal genes and post-translational folding and processing of insecticidal proteins, remain relatively unexplored. The discovery of RNA interference as a gene-specific regulation mechanism offers a new approach for improvement of baculovirus biopesticidal efficacy through genetic modification
Free boundary problems describing two-dimensional pulse recycling and motion in semiconductors
An asymptotic analysis of the Gunn effect in two-dimensional samples of bulk
n-GaAs with circular contacts is presented. A moving pulse far from contacts is
approximated by a moving free boundary separating regions where the electric
potential solves a Laplace equation with subsidiary boundary conditions. The
dynamical condition for the motion of the free boundary is a Hamilton-Jacobi
equation. We obtain the exact solution of the free boundary problem (FBP) in
simple one-dimensional and axisymmetric geometries. The solution of the FBP is
obtained numerically in the general case and compared with the numerical
solution of the full system of equations. The agreement is excellent so that
the FBP can be adopted as the basis for an asymptotic study of the
multi-dimensional Gunn effect.Comment: 19 pages, 9 figures, Revtex. To appear in Phys. Rev.
Synthetic induction of immunogenic cell death by genetic stimulation of endoplasmic reticulum stress.
Cis-diamminedichloridoplatinum(II) (CDDP), commonly referred to as cisplatin, is a chemotherapeutic drug used for the treatment of a wide range of solid cancers. CDDP is a relatively poor inducer of immunogenic cell death (ICD), a cell death modality that converts dying cells into a tumor vaccine, stimulating an immune response against residual cancer cells that permits long-lasting immunity and a corresponding reduction in tumor growth. The incapacity of CDDP to trigger ICD is at least partially due to its failure to stimulate the premortem endoplasmic reticulum (ER)-stress response required for the externalization of the "eat-me" signal calreticulin (CRT) on the surface of dying cancer cells. Here, we developed a murine cancer cell line genetically modified to express the ER resident protein reticulon-1c (Rtn-1c) by virtue of tetracycline induction and showed that enforced Rtn-1c expression combined with CDDP treatment promoted CRT externalization to the surface of cancer cells. In contrast to single agent treatments, the tetracycline-mediated Rtn-1c induction combined with CDDP chemotherapy stimulated ICD as measured by the capacity of dying tumor cells, inoculated into syngenic immunocompetent mice, to mount an immune response to tumor re-challenge 1 week later. More importantly, established tumors, forced to constitutively express Rtn-1c in vivo by continuous treatment with tetracycline, became responsive to CDDP and exhibited a corresponding reduction in the rate of tumor growth. The combined therapeutic effects of Rtn-1c induction with CDDP treatment was only detected in the context of an intact immune system and not in nu/nu mice lacking thymus-dependent T lymphocytes. Altogether, these results indicate that the artificial or "synthetic" induction of immunogenic cell death by genetic manipulation of the ER-stress response can improve the efficacy of chemotherapy with CDDP by stimulating anticancer immunity
Theory of Andreev reflection in a junction with a strongly disordered semiconductor
We study the conduction of a {\sl N~-~Sm~-~S} junction, where {\sl Sm} is a
strongly disordered semiconductor. The differential conductance of this
{\sl N~-~Sm~-~S} structure is predicted to have a sharp peak at . Unlike
the case of a weakly disordered system, this feature persists even in the
absence of an additional (Schottky) barrier on the boundary. The zero-bias
conductance of such a junction is smaller only by a numerical factor
than the conductance in the normal state . Implications for experiments on
gated heterostructures with superconducting leads are discussed.Comment: 4 pages, 2 figures, to appear in Rapid Communication section of Phys.
Rev.
Generalized drift-diffusion model for miniband superlattices
A drift-diffusion model of miniband transport in strongly coupled
superlattices is derived from the single-miniband Boltzmann-Poisson transport
equation with a BGK (Bhatnagar-Gross-Krook) collision term. We use a consistent
Chapman-Enskog method to analyze the hyperbolic limit, at which collision and
electric field terms dominate the other terms in the Boltzmann equation. The
reduced equation is of the drift-diffusion type, but it includes additional
terms, and diffusion and drift do not obey the Einstein relation except in the
limit of high temperatures.Comment: 4 pages, 3 figures, double-column revtex. To appear as RC in PR
Self-sustained spin-polarized current oscillations in multiquantum well structures
Nonlinear transport through diluted magnetic semiconductor nanostructures is investigated. We have considered a II–VI multiquantum well nanostructure whose wells are selectively doped with Mn. The response to a dc voltage bias may be either a stationary or an oscillatory current. We have studied the transition from stationary to time-dependent current as a function of the doping density and the number of quantum wells. Analysis and numerical solution of a nonlinear spin transport model shows that the current in a structure without magnetic impurities is stationary, whereas current oscillations may appear if at least one well contains magnetic impurities. For long structures having two wells with magnetic impurities, a detailed analysis of nucleation of charge dipole domains shows that self-sustained current oscillations are caused by repeated triggering of dipole domains at the magnetic wells and motion towards the collector. Depending on the location of the magnetic wells and the voltage, dipole domains may be triggered at both wells or at only one. In the latter case, the well closer to the collector may inhibit domain motion between the first and the second well inside the structure. Our study could allow design of oscillatory spin-polarized current injectors
Trial Watch: experimental TLR7/TLR8 agonists for oncological indications
Resiquimod (R848) and motolimod (VTX-2337) are second-generation experimental derivatives of imiquimod, an imidazoquinoline with immunostimulatory properties originally approved by the US Food and Drug Administration for the topical treatment of actinic keratosis and genital warts more than 20 years ago. Both resiquimod and motolimod operate as agonists of Toll-like receptor 7 (TLR7) and/or TLR8, in thus far delivering adjuvant-like signals to antigen-presenting cells (APCs). In line with such an activity, these compounds are currently investigated as immunostimulatory agents for the treatment of various malignancies, especially in combination with peptide-based, dendritic cell-based, cancer cell lysate-based, or DNA-based vaccines. Here, we summarize preclinical and clinical evidence recently collected to support the development of resiquimod and motolimod and other TLR7/TLR8 agonists as anticancer agents
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