Moving boundary and photoelastic coupling in GaAs optomechanical resonators

Chip-based cavity optomechanical systems are being considered for applications in sensing, metrology, and quantum information science. Critical to their development is an understanding of how the optical and mechanical modes interact, quantified by the coupling rate $g_{0}$. Here, we develop GaAs optomechanical resonators and investigate the moving dielectric boundary and photoelastic contributions to $g_{0}$. First, we consider coupling between the fundamental radial breathing mechanical mode and a 1550 nm band optical whispering gallery mode in microdisks. For decreasing disk radius from $R=5$ $\mu$m to $R=1$ $\mu$m, simulations and measurements show that $g_{0}$ changes from being dominated by the moving boundary contribution to having an equal photoelastic contribution. Next, we design and demonstrate nanobeam optomechanical crystals in which a $2.5$ GHz mechanical breathing mode couples to a 1550 nm optical mode predominantly through the photoelastic effect. We show a significant (30 $\%$) dependence of $g_{0}$ on the device's in-plane orientation, resulting from the difference in GaAs photoelastic coefficients along different crystalline axes, with fabricated devices exhibiting $g_{\text{0}}/2\pi$ as high as 1.1 MHz for orientation along the [110] axis. GaAs nanobeam optomechanical crystals are a promising system which can combine the demonstrated large optomechanical coupling strength with additional functionality, such as piezoelectric actuation and incorporation of optical gain media

Human occipital and parietal GABA selectively influence visual perception of orientation and size

Gamma-aminobutyric acid (GABA) is the primary inhibitory neurotransmitter in human brain. GABA level varies substantially across individuals and this variability is associated with inter-individual differences in visual perception. However, it remains unclear whether the association between GABA level and visual perception reflects a general influence of visual inhibition, or whether GABA level of different cortical regions selectively influences perception of different visual features. To address this, we studied how GABA level in parietal and occipital cortices related to inter-individual differences in size, orientation, and brightness perception, in a group of healthy young male participants. We used visual contextual illusion as a perceptual assay, since it dissociates perceptual content from stimulus content and its magnitude reflects the effect of visual inhibition. Across individuals, we observed selective correlations between GABA level and the magnitude of contextual illusion. Specifically, parietal GABA level correlated with size illusion magnitude but not with orientation or brightness illusion magnitude; in contrast, occipital GABA level correlated with orientation illusion magnitude but not with size or brightness illusion magnitude. Our findings reveal a region- and feature-dependent influence of GABA level on human visual perception. Parietal and occipital cortices contain, respectively, topographic maps of size and orientation preference in which neural responses to sizes or orientations are modualted by intra-regional lateral connections. We propose that these lateral connections may underlie the selective influence of GABA level on visual feature perception.SIGNIFICANCE STATEMENTGamma-aminobutyric acid (GABA), the primary inhibitory neurotransmitter in human visual system, varies substantially across individuals and this variability is linked to inter-individual differences in many aspects of visual perception. The widespread influence of GABA raises the question of whether inter-individual variability in GABA reflects an overall variability in visual inhibition and has a general influence on visual perception, or whether GABA level of different cortical regions has selective influence on perception of different visual features. Here we report a region- and feature-dependent influence of GABA level on human visual perception. Our findings suggest that GABA level of a cortical region selectively influences perception of visual features that are topographically mapped in this region through intra-regional lateral connections

The role of N∗(1535)N^*(1535) in pp→ppϕpp \to pp \phi and π−p→nϕ\pi^- p \to n \phi reactions

The near threshold $\phi$ meson production in proton-proton and $\pi^- p$ collisions is studied with the assumption that the production mechanism is due to the sub-$N\phi$-threshold $N^*(1535)$ resonance. The $\pi^0$, $\eta$ and $\rho^0$-meson exchanges for proton-proton collisions are considered. It is shown that the contribution to the $pp \to pp \phi$ reaction from the t-channel $\pi^0$ meson exchange is dominant. With a significant $N^*(1535)N\phi$ coupling ($g^2_{N^*(1535)N \phi}/4 \pi$ = 0.13), both $pp \to pp \phi$ and $\pi^- p \to n \phi$ data are very well reproduced. The significant coupling of the $N^*(1535)$ resonance to $N \phi$ is compatible with previous indications of a large $s \bar{s}$ component in the quark wave function of the $N^*(1535)$ resonance and may be the real origin of the significant enhancement of the $\phi$ production over the naive OZI-rule predictions.Comment: 15 pages, 6 figure

Differential-difference system related to toroidal Lie algebra

We present a novel differential-difference system in (2+1)-dimensional space-time (one discrete, two continuum), arisen from the Bogoyavlensky's (2+1)-dimensional KdV hierarchy. Our method is based on the bilinear identity of the hierarchy, which is related to the vertex operator representation of the toroidal Lie algebra \sl_2^{tor}.Comment: 10 pages, 4 figures, pLaTeX2e, uses amsmath, amssymb, amsthm, graphic

Quantifying gas emissions from the "Millennium Eruption" of Paektu volcano, Democratic Peoples Republic of Korea/China

Paektu volcano (Changbaishan) is a rhyolitic caldera that straddles the border between the Democratic People’s Republic of Korea and China. Its most recent large eruption was the Millennium Eruption (ME; 23 km$^{3}$ dense rock equivalent) circa 946 CE, which resulted in the release of copious magmatic volatiles (H$_{2}$O, CO$_{2}$, sulfur, and halogens). Accurate quantification of volatile yield and composition is critical in assessing volcanogenic climate impacts but is challenging, particularly for events before the satellite era. We use a geochemical technique to quantify volatile composition and upper bounds to yields for the ME by examining trends in incompatible trace and volatile element concentrations in crystal-hosted melt inclusions. We estimate that the ME could have emitted as much as 45 Tg of S to the atmosphere. This is greater than the quantity of S released by the 1815 eruption of Tambora, which contributed to the “year without a summer.” Our maximum gas yield estimates place the ME among the strongest emitters of climate-forcing gases in the Common Era. However, ice cores from Greenland record only a relatively weak sulfate signal attributed to the ME. We suggest that other factors came into play in minimizing the glaciochemical signature. This paradoxical case in which high S emissions do not result in a strong glacial sulfate signal may present a way forward in building more https://symplectic.admin.cam.ac.uk/objectedit.html?cid=1&oid=876954generalized models for interpreting which volcanic eruptions have produced large climate impacts.K.I. was supported by the NSF under award no. 1349486 and by AAAS. Fieldwork was supported by the Richard Lounsbery Foundation

Aldose reductase regulates microglia/macrophages polarization through the cAMP response element-binding protein after spinal cord injury in mice.

Inflammatory reactions are the most critical pathological processes occurring after spinal cord injury (SCI). Activated microglia/macrophages have either detrimental or beneficial effects on neural regeneration based on their functional polarized M1/M2 subsets. However, the mechanism of microglia/macrophage polarization to M1/M2 at the injured spinal cord environment remains unknown. In this study, wild-type (WT) or aldose reductase (AR)-knockout (KO) mice were subjected to SCI by a spinal crush injury model. The expression pattern of AR, behavior tests for locomotor activity, and lesion size were assessed at between 4 h and 28 days after SCI. We found that the expression of AR is upregulated in microglia/macrophages after SCI in WT mice. In AR KO mice, SCI led to smaller injury lesion areas compared to WT. AR deficiency-induced microglia/macrophages induce the M2 rather than the M1 response and promote locomotion recovery after SCI in mice. In the in vitro experiments, microglia cell lines (N9 or BV2) were treated with the AR inhibitor (ARI) fidarestat. AR inhibition caused 4-hydroxynonenal (HNE) accumulation, which induced the phosphorylation of the cAMP response element-binding protein (CREB) to promote Arg1 expression. KG501, the specific inhibitor of phosphorylated CREB, could cancel the upregulation of Arg1 by ARI or HNE stimulation. Our results suggest that AR works as a switch which can regulate microglia by polarizing cells to either the M1 or the M2 phenotype under M1 stimulation based on its states of activity. We suggest that inhibiting AR may be a promising therapeutic method for SCI in the future

Sod2 haploinsufficiency does not accelerate aging of telomere dysfunctional mice

Telomere shortening represents a causal factor of cellular senescence. At the same time, several lines of evidence indicate a pivotal role of oxidative DNA damage for the aging process in vivo. A causal connection between the two observations was suggested by experiments showing accelerated telomere shorting under conditions of oxidative stress in cultured cells, but has never been studied in vivo. We therefore have analysed whether an increase in mitochondrial derived oxidative stress in response to heterozygous deletion of superoxide dismutase (Sod2+/-) would exacerbate aging phenotypes in telomere dysfunctional (mTerc-/-) mice. Heterozygous deletion of Sod2 resulted in reduced SOD2 protein levels and increased oxidative stress in aging telomere dysfunctional mice, but this did not lead to an increase in basal levels of oxidative nuclear DNA damage, an accumulation of nuclear DNA breaks, or an increased rate of telomere shortening in the mice. Moreover, heterozygous deletion of Sod2 did not accelerate the depletion of stem cells and the impairment in organ maintenance in aging mTerc-/- mice. In agreement with these observations, Sod2 haploinsufficiency did not lead to a further reduction in lifespan of mTerc-/- mice. Together, these results indicate that a decrease in SOD2-dependent antioxidant defence does not exacerbate aging in the context of telomere dysfunction

miR-9 and miR-124 synergistically affect regulation of dendritic branching via the AKT/GSK3β pathway by targeting Rap2a

A single microRNA (miRNA) can regulate expression of multiple proteins, and expression of an individual protein may be controlled by numerous miRNAs. This regulatory pattern strongly suggests that synergistic effects of miRNAs play critical roles in regulating biological processes. miR-9 and miR-124, two of the most abundant miRNAs in the mammalian nervous system, have important functions in neuronal development. In this study, we identified the small GTP-binding protein Rap2a as a common target of both miR-9 and miR-124. miR-9 and miR-124 together, but neither miRNA alone, strongly suppressed Rap2a, thereby promoting neuronal differentiation of neural stem cells (NSCs) and dendritic branching of differentiated neurons. Rap2a also diminished the dendritic complexity of mature neurons by decreasing the levels of pAKT and pGSK3β. Our results reveal a novel pathway in which miR-9 and miR-124 synergistically repress expression of Rap2a to sustain homeostatic dendritic complexity during neuronal development and maturation

Photoconductivity of biased graphene

Graphene is a promising candidate for optoelectronic applications such as photodetectors, terahertz imagers, and plasmonic devices. The origin of photoresponse in graphene junctions has been studied extensively and is attributed to either thermoelectric or photovoltaic effects. In addition, hot carrier transport and carrier multiplication are thought to play an important role. Here we report the intrinsic photoresponse in biased but otherwise homogeneous graphene. In this classic photoconductivity experiment, the thermoelectric effects are insignificant. Instead, the photovoltaic and a photo-induced bolometric effect dominate the photoresponse due to hot photocarrier generation and subsequent lattice heating through electron-phonon cooling channels respectively. The measured photocurrent displays polarity reversal as it alternates between these two mechanisms in a backgate voltage sweep. Our analysis yields elevated electron and phonon temperatures, with the former an order higher than the latter, confirming that hot electrons drive the photovoltaic response of homogeneous graphene near the Dirac point