Gate Voltage Controllable Non-Equilibrium and Non-Ohmic Behavior in Suspended Carbon Nanotubes

In this work, we measure the electrical conductance and temperature of individual, suspended quasi-metallic single-walled carbon nanotubes under high voltage biases using Raman spectroscopy, while varying the doping conditions with an applied gate voltage. By applying a gate voltage, the high-bias conductance can be switched dramatically between linear (Ohmic) behavior and nonlinear behavior exhibiting negative differential conductance (NDC). Phonon populations are observed to be in thermal equilibrium under Ohmic conditions but switch to nonequilibrium under NDC conditions. A typical Landauer transport model assuming zero bandgap is found to be inadequate to describe the experimental data. A more detailed model is presented, which incorporates the doping dependence in order to fit this data

Spatially-Resolved Temperature Measurements of Electrically-Heated Carbon Nanotubes

Spatially-resolved Raman spectra of individual pristine suspended carbon nanotubes are observed under electrical heating. The Raman G+ and G- bands show unequal temperature profiles. The preferential heating is more pronounced in short nanotubes (2 um) than in long nanotubes (5 um). These results are understood in terms of the decay and thermalization of non-equilibrium phonons, revealing the mechanism of thermal transport in these devices. The measurements also enable a direct estimate of thermal contact resistances and the spatial variation of thermal conductivity.Comment: To appear in Phys. Rev. Let

Direct Observation of Broadband Coating Thermal Noise in a Suspended Interferometer

We have directly observed broadband thermal noise in silica/tantala coatings in a high-sensitivity Fabry-Perot interferometer. Our result agrees well with the prediction based on indirect, ring-down measurements of coating mechanical loss, validating that method as a tool for the development of advanced interferometric gravitational-wave detectors.Comment: Final version synchronized with publication in Phys. Lett.

Host Species Restriction of Middle East Respiratory Syndrome Coronavirus through Its Receptor, Dipeptidyl Peptidase 4

Middle East respiratory syndrome coronavirus (MERS-CoV) emerged in 2012. Recently, the MERS-CoV receptor dipeptidyl peptidase 4 (DPP4) was identified and the specific interaction of the receptor-binding domain (RBD) of MERS-CoV spike protein and DPP4 was determined by crystallography. Animal studies identified rhesus macaques but not hamsters, ferrets, or mice to be susceptible for MERS-CoV. Here, we investigated the role of DPP4 in this observed species tropism. Cell lines of human and nonhuman primate origin were permissive of MERS-CoV, whereas hamster, ferret, or mouse cell lines were not, despite the presence of DPP4. Expression of human DPP4 in nonsusceptible BHK and ferret cells enabled MERS-CoV replication, whereas expression of hamster or ferret DPP4 did not. Modeling the binding energies of MERS-CoV spike protein RBD to DPP4 of human (susceptible) or hamster (nonsusceptible) identified five amino acid residues involved in the DPP4-RBD interaction. Expression of hamster DPP4 containing the five human DPP4 amino acids rendered BHK cells susceptible to MERS-CoV, whereas expression of human DPP4 containing the five hamster DPP4 amino acids did not. Using the same approach, the potential of MERS-CoV to utilize the DPP4s of common Middle Eastern livestock was investigated. Modeling of the DPP4 and MERS-CoV RBD interaction predicted the ability of MERS-CoV to bind the DPP4s of camel, goat, cow, and sheep. Expression of the DPP4s of these species on BHK cells supported MERS-CoV replication. This suggests, together with the abundant DPP4 presence in the respiratory tract, that these species might be able to function as a MERS-CoV intermediate reservoir

The Middle East Respiratory Syndrome Coronavirus (MERS-CoV) Does Not Replicate in Syrian Hamsters

In 2012 a novel coronavirus, MERS-CoV, associated with severe respiratory disease emerged in the Arabian Peninsula. To date, 55 human cases have been reported, including 31 fatal cases. Several of the cases were likely a result of human-to-human transmission. The emergence of this novel coronavirus prompts the need for a small animal model to study the pathogenesis of this virus and to test the efficacy of potential intervention strategies. In this study we explored the use of Syrian hamsters as a small animal disease model, using intratracheal inoculation and inoculation via aerosol. Clinical signs of disease, virus replication, histological lesions, cytokine upregulation nor seroconversion were observed in any of the inoculated animals, indicating that MERS-CoV does not replicate in Syrian hamsters

Hot Phonons in an Electrically Biased Graphene Constriction

Phonon carrier interactions can have significant impact on device performance. They can be probed by measuring the phonon lifetime, which reflects the interaction strength of a phonon with other quasi-particles in particular charge carriers as well as its companion phonons. The carrier phonon and phonon-phonon contributions to the phonon lifetime can be disentangled from temperature dependent studies. Here, we address the importance of phonon carrier interactions in Joule-heated graphene constrictions in order to contribute to the understanding of energy dissipation in graphene based electronic devices. We demonstrate that gapless graphene grants electron phonon interactions uncommon significance in particular at low carrier density. In conventional semiconductors, the bandgap usually prevents the decay of phonons through electron-hole generation and also in metals or other semimetals the Fermi temperature is excessively large to enter the regime where electron phonon coupling plays such a dominant role as in graphene in the investigated phonon temperature regime from 300 to 1600 K.Comment: Nano Letters (Web publication on 30th Dec. 2009, DOI:10.1021/nl903167f

Thermal infrared emission reveals the Dirac point movement in biased graphene

Graphene is a 2-dimensional material with high carrier mobility and thermal conductivity, suitable for high-speed electronics. Conduction and valence bands touch at the Dirac point. The absorptivity of single-layer graphene is 2.3%, nearly independent of wavelength. Here we investigate the thermal radiation from biased graphene transistors. We find that the emission spectrum of single-layer graphene follows that of a grey body with constant emissivity (1.6 \pm 0.8)%. Most importantly, we can extract the temperature distribution in the ambipolar graphene channel, as confirmed by Stokes/anti-Stokes measurements. The biased graphene exhibits a temperature maximum whose location can be controlled by the gate voltage. We show that this peak in temperature reveals the spatial location of the minimum in carrier density, i.e. the Dirac point.Comment: Accepted in principle at Nature Nanotechnolog

SARS-Like coronavirus WIV1-CoV does not replicate in Egyptian fruit bats (Rousettus aegyptiacus)

Severe acute respiratory syndrome (SARS)-like WIV1-coronavirus (CoV) was first isolated from Rhinolophus sinicus bats and can use the human angiotensin converting enzyme 2 (ACE2) receptor. In the current study, we investigate the ability of WIV1-CoV to infect Rousettus aegyptiacus bats. No clinical signs were observed throughout the experiment. Furthermore, only four oropharyngeal swabs and two respiratory tissues, isolated on day 3 post inoculation, were found positive for viral RNA. Two out of twelve bats showed a modest increase in coronavirus specific antibodies post challenge. In conclusion, WIV1-CoV was unable to cause a robust infection in Rousettus aegyptiacus bats