Ultrafast Transient Spectroscopy of Trans-Polyacetylene in the Midinfrared Spectral Range

Trans-polyacetylene [t-(CH)(x)] possesses twofold ground state degeneracy. Using the Su-Schrieffer-Heeger Hamiltonian, scientists predicted charged solitons to be the primary photoexcitations in t-(CH)(x); this prediction, however, has led to sharp debate. To resolve this saga, we use subpicosecond transient photomodulation spectroscopy in the mid-IR spectral range (0.1-1.5 eV) in neat t-(CH)(x) thin films. We show that odd-parity singlet excitons are the primary photoexcitations in t-(CH)(x), similar to many other nondegenerate pi-conjugated polymers. The exciton transitions are characterized by two photoinduced absorption (PA) bands at 0.38 and 0.6 eV, and an associated photoluminescence band at similar to 1.5 eV having similar polarization memory. The primary excitons undergo internal conversion within similar to 100 fs to an even parity (dark) singlet exciton with a PA band at similar to 1.4 eV. We also find ultrafast photogeneration of charge polarons when pumping deep into the polymer continuum band, which are characterized by two other PA bands in the mid-IR and associated photoinduced IR vibrational modes

Observation of near-inertial wave reflections within the thermostad layer of an anticyclonic mesoscale eddy

Author Posting. © American Geophysical Union, 2010. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Geophysical Research Letters 37 (2010): L01606, doi:10.1029/2009GL041601.Moored current observations in the southwestern East/Japan Sea of 16.5 months duration clearly captured two episodes of downward phase propagation (upward energy propagation) of near-inertial waves (NIWs). Time series of temperature and velocity from the mooring and ancillary information indicate that the mooring was located near the center of an anticyclonic eddy during these events. Considering the typical vertical structure of quasi-permanent eddy features in the region, the observed downward phase propagation appeared to occur within the seasonal thermocline and upper thermostad of the anticyclonic mesoscale eddy. Ray tracing simulation of NIW using the observed subinertial currents suggests that the upward energy propagation is caused by the reflection of the NIWs within the thermostad of the anticyclonic eddy, where the effect of the vertical shear of subinertial horizontal currents is larger than the buoyancy effect in controlling the propagation of NIWs.This work was supported by grants from the Ministry of Land, Transport, and Maritime Affairs (Ocean Climate Variability Program), and the US NSF, grant OCE-0647949 to RWS

Photoswitchable Particles for On‐Demand Degradation and Triggered Release

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/100171/1/smll_201201921_sm_suppl.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/100171/2/3051_ftp.pd

Bmi-1 is required for maintenance of adult self-renewing haematopoietic stem cells

A central issue in stem cell biology is to understand the mechanisms that regulate the self-renewal of haematopoietic stem cells (HSCs), which are required for haematopoiesis to persist for the lifetime of the animal(1). We found that adult and fetal mouse and adult human HSCs express the proto-oncogene Bmi-1. The number of HSCs in the fetal liver of Bmi-1(-/-) mice(2) was normal. In postnatal Bmi-1(-/-) mice, the number of HSCs was markedly reduced. Transplanted fetal liver and bone marrow cells obtained from Bmi-1(-/-) mice were able to contribute only transiently to haematopoiesis. There was no detectable self-renewal of adult HSCs, indicating a cell autonomous defect in Bmi-1(-/-) mice. A gene expression analysis revealed that the expression of stem cell associated genes(3), cell survival genes, transcription factors, and genes modulating proliferation including p16(Ink4a) and p19(Arf) was altered in bone marrow cells of the Bmi-1(-/-) mice. Expression of p16(Ink4a) and p19(Arf) in normal HSCs resulted in proliferative arrest and p53-dependent cell death, respectively. Our results indicate that Bmi-1 is essential for the generation of self-renewing adult HSCs.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/62508/1/nature01587.pd

A self-tuning mechanism in (3+p)d gravity-scalar theory

We present a new type of self-tuning mechanism for ($3+p$)d brane world models in the framework of gravity-scalar theory. This new type of self-tuning mechanism exhibits a remarkable feature. In the limit $g_s \to 0$, $g_s$ being the string coupling, the geometry of bulk spacetime remains virtually unchanged by an introduction of the Standard Model(SM)-brane, and consequently it is virtually unaffected by quantum fluctuations of SM fields with support on the SM-brane. Such a feature can be obtained by introducing Neveu-Schwarz(NS)-brane as a background brane on which our SM-brane is to be set. Indeed, field equations naturally suggest the existence of the background NS-brane. Among the given such models, of the most interest is the case with $\Lambda=0$, where $\Lambda$ represents the bulk cosmological constant. This model contains a pair of coincident branes (of the SM- and the NS-branes), one of which is a codimension-2 brane placed at the origin of 2d transverse space ($\equiv \Sigma_2$), another a codimension-1 brane placed at the edge of $\Sigma_2$. These two branes are (anti) T-duals of each other, and one of them may be identified as our SM-brane plus the background NS-brane. In the presence of the background NS-brane (and in the absence of $\Lambda$), the 2d transverse space $\Sigma_2$ becomes an orbifold $R_2 /Z_n$ with an appropriate deficit angle. But this is only possible if the ($3+p$)d Planck scale $M_{3+p}$ and the string scale $M_s$($\equiv 1/\sqrt{\alpha^{\prime}}$) are of the same order, which accords with the hierarchy assumption \cite{1,2,3} that the electroweak scale $m_{EW}$ is the only short distance scale existing in nature

Targeting and Blocking B7 Costimulatory Molecules on Antigen-Presenting Cells Using CTLA4Ig-Conjugated Liposomes: In Vitro Characterization and in Vivo Factors Affecting Biodistribution

Purpose. CTLA4Ig, a fusion protein of CTLA-4 and Fc of immunoglobulin (Ig) heavy chain, inhibits the essential costimulatory signal for full T cell activation via blocking the interaction between CD28 and B7 molecules and renders T cell nonresponsiveness. CTLA4Ig has been used to control deleterious T cell activation in many experimental systems. We hypothesized that by conjugating CTLA4Ig to liposomes the efficacy of CTLA4Ig could be enhanced through multivalent ligand effect, superior targetability, and modification of the fate of ligated costimulatory molecules.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/41500/1/11095_2004_Article_468685.pd