Feedback Regulation and its Efficiency in Biochemical Networks

Intracellular biochemical networks fluctuate dynamically due to various internal and external sources of fluctuation. Dissecting the fluctuation into biologically relevant components is important for understanding how a cell controls and harnesses noise and how information is transferred over apparently noisy intracellular networks. While substantial theoretical and experimental advancement on the decomposition of fluctuation was achieved for feedforward networks without any loop, we still lack a theoretical basis that can consistently extend such advancement to feedback networks. The main obstacle that hampers is the circulative propagation of fluctuation by feedback loops. In order to define the relevant quantity for the impact of feedback loops for fluctuation, disentanglement of the causally interlocked influence between the components is required. In addition, we also lack an approach that enables us to infer non-perturbatively the influence of the feedback to fluctuation as the dual reporter system does in the feedforward network. In this work, we resolve these problems by extending the work on the fluctuation decomposition and the dual reporter system. For a single-loop feedback network with two components, we define feedback loop gain as the feedback efficiency that is consistent with the fluctuation decomposition for feedforward networks. Then, we clarify the relation of the feedback efficiency with the fluctuation propagation in an open-looped FF network. Finally, by extending the dual reporter system, we propose a conjugate feedback and feedforward system for estimating the feedback efficiency only from the statistics of the system non-perturbatively

Excitons and biexcitons in symmetric electron-hole bilayers

Symmetric electron-hole bilayer systems have been studied at zero temperature using the diffusion quantum Monte Carlo method. A flexible trial wave function is used that can describe fluid, excitonic and biexcitonic phases. We calculate condensate fractions and pair correlation functions for a large number of densities rs and layer separations d. At small d we find a one-component fluid phase, an excitonic fluid phase, and a biexcitonic fluid phase, and the transitions among them appear to be continuous. At d = 0, excitons appear to survive down to about rs = 0.5 a.u., and biexcitons form at rs > 2.5 a.u.Comment: 5 pages, 4 figure

Induction of specific tolerance by intrathymic injection of recipient muscle cells transfected with donor class I major histocompatibility complex.

Induction of tolerance to allogeneic MHC antigens has been a goal in the field of transplantation because it would reduce or eliminate the need for generalized immunosuppression. Although encouraging results have been obtained in experimental models by exposing recipient thymus to donor cells before transplantation, donor cells are not typically available at that time, and the donor antigens responsible for the effect are poorly defined. In the present study, thymic tolerance was demonstrated without using donor cells. Recipient thymus was injected before transplantation with autologous myoblasts and myotubes that were genetically modified to express allogeneic donor-type MHC class I antigen. Donor-specific unresponsiveness was induced to a completely MHC-disparate liver transplant and to a subsequent donor-type cardiac allograft, but not a third-party allograft. In vitro, recipient CTL demonstrated a 10-fold reduction in killing of donor cells, but not of third-party cells. Our results demonstrate: (1) that recipient muscle cells can be genetically engineered to induce donor-specific unresponsiveness when given intrathymically, and (2) transfected recipient cells expressing only donor MHC class I antigen can induce tolerance to a fully allogeneic donor

Nonthermal Emission Associated with Strong AGN Outbursts at the Centers of Galaxy Clusters

Recently, strong AGN outbursts at the centers of galaxy clusters have been found. Using a simple model, we study particle acceleration around a shock excited by an outburst and estimate nonthermal emission from the accelerated particles. We show that emission from secondary electrons is consistent with the radio observations of the minihalo in the Perseus cluster, if there was a strong AGN outburst >~10^8 yrs ago with an energy of ~1.8x10^62 erg. The validity of our model depends on the frequency of the large outbursts. We also estimate gamma-ray emission from the accelerated particles and show that it could be detected with GLAST.Comment: Accepted for publication in ApJ

Selective entanglement breaking

We discuss the cases where local decoherence selectively degrades one type of entanglement more than other types. A typical case is called state ordering change, in which two input states with different amounts of entanglement undergoes a local decoherence and the state with the larger entanglement results in an output state with less entanglement than the other output state. We are also interested in a special case where the state with the larger entanglement evolves to a separable state while the other output state is still entangled, which we call selective entanglement breaking. For three-level or larger systems, it is easy to find examples of the state ordering change and the selective entanglement breaking, but for two-level systems it is not trivial whether such situations exist. We present a new strategy to construct examples of two-qubit states exhibiting the selective entanglement breaking regardless of entanglement measure. We also give a more striking example of the selective entanglement breaking in which the less entangled input state has only an infinitesimal amount of entanglement.Comment: 6 pages, 2 figure

Biodegradable, Low Biological Toxicity Radiographic Contrast Medium and Method of X-Ray Imaging

A biodegradable, low biological toxicity, particulate radiographic contrast medium comprises biodegradable polymeric spheres of average molecular weight average diameter about 10-1,000 nm or about 0.01-1.0 micron carrying in at least radiographic contrasting amount of a radiographically opaque element. A method of obtaining a tomographic image of the body portion of a subject comprises administering to the subject a radiographically-detectable amount of the biodegradable, low-toxicity radiographic medium of claim 1; allowing for the spheres to be taken-up by the body portion; and X-raying an area comprising the body portion. A method of improving the contrast of a tomographic image of a body portion of a subject comprises administering to the subject a radiographically-detectable amount of the biodegradable, low-toxicity radiographic medium of claim 1; allowing for the spheres to be selectively taken-up by the body portion; and X-raying an area comprising the body portion

Near-infrared circular polarization survey in star-forming regions : Correlations and trends

We have conducted a systematic near-infrared circular polarization (CP) survey in star-forming regions, covering high-mass, intermediate-mass, and low-mass young stellar objects. All the observations were made using the SIRPOL imaging polarimeter on the Infrared Survey Facility 1.4 m telescope at the South African Astronomical Observatory. We present the polarization properties of 10 sub-regions in 6 star-forming regions. The polarization patterns, extents, and maximum degrees of linear and circular polarizations are used to determine the prevalence and origin of CP in the star-forming regions. Our results show that the CP pattern is quadrupolar in general, the CP regions are extensive, up to 0.65 pc, the CP degrees are high, up to 20%, and the CP degrees decrease systematically from high- to low-mass young stellar objects. The results are consistent with dichroic extinction mechanisms generating the high degrees of CP in star-forming regions.Peer reviewe