arXiv subjects

C. Jiang

Publications and source records attributed to C. Jiang.

49 records · Page 3Linked to original sources

arXiv2013

All-Metallic Electrically-Gated Tantalum Diselenide Switches and Logic Circuits

We report the fabrication and performance of all-metallic three-terminal devices with tantalum diselenide thin-film conducting channels. For this proof-of-concept demonstration, the layers of 2H-TaSe2 were exfoliated mechanically from single crystals grown by the chemical vapor transport method. Devices with nanometer-scale thicknesses exhibit strongly non-linear current-voltage characteristics, unusual optical response, and electrical gating at room temperature. We have found that the drain-source current in thin-film 2H-TaSe2-Ti/Au devices reproducibly shows an abrupt transition from a highly resistive to a conductive state, with the threshold tunable via the gate voltage. Such current-voltage characteristics can be used in principle for implementing radiation-hard all-metallic logic circuits. These results may open new application space for thin films of van der Waals materials.

cond-mat.mes-hall↗

arXiv2013

Phonon and Thermal Properties of Exfoliated Tantalum Diselenide Thin Films

We report on the phonon and thermal properties of thin films of tantalum diselenide (2H-TaSe2) obtained via the graphene-like mechanical exfoliation of crystals grown by chemical vapor transport. The ratio of the intensities of the Raman peak from the Si substrate and the E2g peak of TaSe2 presents a convenient metric for quantifying film thickness. The temperature coefficients for two main Raman peaks, A1g and E2g, are -0.013 and -0.0097 cm-1/oC, respectively. The Raman optothermal measurements indicate that the room temperature thermal conductivity in these films decreases from its bulk value of ~16 W/mK to ~9 W/mK in 45-nm thick films. The measurement of electrical resistivity of the field-effect devices with TaSe2 channels indicates that heat conduction is dominated by acoustic phonons in these van der Waals films. The scaling of thermal conductivity with the film thickness suggests that the phonon scattering from the film boundaries is substantial despite the sharp interfaces of the mechanically cleaved samples. These results are important for understanding the thermal properties of thin films exfoliated from TaSe2 and other metal dichalcogenides, as well as for evaluating self-heating effects in devices made from such materials.

cond-mat.mtrl-sci↗

arXiv2013

A new investigation of electron neutrino appearance oscillations with improved sensitivity in the MiniBooNE+ experiment

We propose the addition of scintillator to the existing MiniBooNE detector to allow a test of the neutral-current/charged-current (NC/CC) nature of the MiniBooNE low-energy excess. Scintillator will enable the reconstruction of 2.2 MeV $γ$s from neutron-capture on protons following neutrino interactions. Low-energy CC interactions where the oscillation excess is observed should have associated neutrons with less than a 10% probability. This is in contrast to the NC backgrounds that should have associated neutrons in approximately 50% of events. We will measure these neutron fractions with $ν_μ$ CC and NC events to eliminate that systematic uncertainty. This neutron-fraction measurement requires $6.5\times10^{20}$ protons on target delivered to MiniBooNE with scintillator added in order to increase the significance of an oscillation excess to over $5σ$. This new phase of MiniBooNE will also enable additional important studies such as the spin structure of nucleon ($Δs$) via NC elastic scattering, a low-energy measurement of the neutrino flux via $\numu ^{12}C \rightarrow μ^{-} ^{12}N_\textrm{g.s.}$ scattering, and a test of the quasielastic assumption in neutrino energy reconstruction. These topics will yield important, highly-cited results over the next 5 years for a modest cost, and will help to train Ph.D. students and postdocs. This enterprise offers complementary information to that from the upcoming liquid Argon based MicroBooNE experiment. In addition, MicroBooNE is scheduled to receive neutrinos in early 2014, and there is minimal additional cost to also deliver beam to MiniBooNE.

hep-ex↗

arXiv2013

Discovery Signal Design and Its Application to Peer-to-Peer Communications in OFDMA Cellular Networks

This paper proposes a unique discovery signal as an enabler of peer-to-peer (P2P) communication which overlays a cellular network and shares its resources. Applying P2P communication to cellular network has two key issues: 1. Conventional ad hoc P2P connections may be unstable since stringent resource and interference coordination is usually difficult to achieve for ad hoc P2P communications; 2. The large overhead required by P2P communication may offset its gain. We solve these two issues by using a special discovery signal to aid cellular network-supervised resource sharing and interference management between cellular and P2P connections. The discovery signal, which facilitates efficient neighbor discovery in a cellular system, consists of un-modulated tones transmitted on a sequence of OFDM symbols. This discovery signal not only possesses the properties of high power efficiency, high interference tolerance, and freedom from near-far effects, but also has minimal overhead. A practical discovery-signal-based P2P in an OFDMA cellular system is also proposed. Numerical results are presented which show the potential of improving local service and edge device performance in a cellular network.

cs.IT↗

arXiv2012

Low Mass WIMP Searches with a Neutrino Experiment: A Proposal for Further MiniBooNE Running

A proposal submitted to the FNAL PAC is described to search for light sub-GeV WIMP dark matter at MiniBooNE. The possibility to steer the beam past the target and into an absorber leads to a significant reduction in neutrino background, allowing for a sensitive search for elastic scattering of WIMPs off nucleons or electrons in the detector. Dark matter models involving a vector mediator can be probed in a parameter region consistent with the required thermal relic density, and which overlaps the region in which these models can resolve the muon g-2 discrepancy. Estimates of signal significance are presented for various operational modes and parameter points. The experimental approach outlined for applying MiniBooNE to a light WIMP search may also be applicable to other neutrino facilities.

hep-ex↗

arXiv2012

Red Giant Oscillations: Stellar Models and Mode Frequency Calculations

We present preliminary results on modelling KIC 7693833, the so far most metal-poor red-giant star observed by {\it Kepler}. From time series spanning several months, global oscillation parameters and individual frequencies were obtained and compared to theoretical calculations. Evolution models are calculated taking into account spectroscopic and asteroseismic constraints. The oscillation frequencies of the models were computed and compared to the {\it Kepler} data. In the range of mass computed, there is no preferred model, giving an uncertainty of about 30 K in $T_eff$, 0.02 dex in $\log g$, $0.7 \,R_\odot$ in radius and of about 2.5 Gyr in age.

astro-ph.SR↗

arXiv2012

Letter of Intent: A new investigation of numu to nue oscillations with improved sensitivity in an enhanced MiniBooNE experiment

We propose adding 300 mg/l PPO to the existing MiniBooNE detector mineral oil to increase the scintillation response. This will allow the detection of associated neutrons and increase sensitivity to final-state nucleons in neutrino interactions. This increased capability will enable an independent test of whether the current excess seen in the MiniBooNE oscillation search is signal or background. In addition it will enable other neutrino interaction measurements to be made including a search for the strange-quark contribution to the nucleon spin Delta s and a low-energy measurement of charged-current quasielastic scattering.

hep-ex↗

arXiv2012

Distributed Dynamic Inter-Cell Interference Management for Femtocell Networks Using Over-the-Air Single-Tone Signaling

Femtocell networks are promising for not only improving the coverage but also increasing the capacity of current cellular networks. The interference-limited reality in femtocell networks makes interference management (IM) the key to maintaining the quality of service and fairness in femtocell networks. Over-the-air signaling is one of the most effective means for fast distributed dynamic IM. However, the design of this type of signal is challenging. In this paper, we address the challenges and propose an effective solution, referred to as single-tone signaling (STS). The proposed STS scheme possesses many highly desirable properties, such as no dedicated resource requirement (no system overhead), no near-far effect, no inter-signal interference, and immunity to synchronization error. In addition, the proposed STS signal provides a means for high quality wideband channel estimation for the use of coordinated techniques, such as coordinated beamforming. Based on the proposed STS, two distributed dynamic IM schemes, ON/OFF power control and SLNR (signal-to-leakage-plus-noise-ratio)-based transmitter beam coordination, are proposed. Simulation results show significant performance improvement as a result of the use of STS-based IM schemes.

cs.IT↗

arXiv2011

Coded Single-Tone Signaling and Its Application to Resource Coordination and Interference Management in Femtocell Networks

Resource coordination and interference management is the key to achieving the benefits of femtocell networks. Over-the-air signaling is one of the most effective means for distributed dynamic resource coordination and interference management. However, the design of this type of signal is challenging. In this paper, we address the challenges and propose an effective solution, referred to as coded single-tone signaling (STS). The proposed coded STS scheme possesses certain highly desirable properties, such as no dedicated resource requirement (no overhead), no near-and-far effect, no inter-signal interference (no multi-user interference), low peak-to-average power ratio (deep coverage). In addition, the proposed coded STS can fully exploit frequency diversity and provides a means for high quality wideband channel estimation. The coded STS design is demonstrated through a concrete numerical example. Performance of the proposed coded STS and its effect on cochannel traffic channels are evaluated through simulations.

cs.IT↗

arXiv2011

Efficient Neighbor Discovery for Proximity-Aware Networks

In this work, we propose a fast and energy-efficient neighbor discovery scheme for proximity-aware networks such as wireless ad hoc networks. Discovery efficiency is accomplished by the use of a special discovery signal that provides random multiple access with low transmit power consumption and low synchronization requirement.

cs.IT↗

arXiv2010

MIMO Precoding Using Rotating Codebooks

Next generation wireless communications rely on multiple input multiple output (MIMO) techniques to achieve high data rates. Feedback of channel information can be used in MIMO precoding to fully activate the strongest channel modes and improve MIMO performance. Unfortunately, the bandwidth of the control channel via which the feedback is conveyed is severely limited. An important issue is how to improve the MIMO precoding performance with minimal feedback. In this letter, we present a method that uses a rotating codebook technique to effectively improve the precoding performance without the need of increasing feedback overhead. The basic idea of the rotating codebook precoding is to expend the effective precoding codebook size via rotating multiple codebooks so that the number of feedback bits remains unchanged. Simulation results are presented to show the performance gain of the proposed rotating codebook precoding over the conventional precoding.

cs.IT↗

arXiv2010

Solar-like oscillations in low-luminosity red giants: first results from Kepler

We have measured solar-like oscillations in red giants using time-series photometry from the first 34 days of science operations of the Kepler Mission. The light curves, obtained with 30-minute sampling, reveal clear oscillations in a large sample of G and K giants, extending in luminosity from the red clump down to the bottom of the giant branch. We confirm a strong correlation between the large separation of the oscillations (Delta nu) and the frequency of maximum power (nu_max). We focus on a sample of 50 low-luminosity stars (nu_max > 100 muHz, L <~ 30 L_sun) having high signal-to-noise ratios and showing the unambiguous signature of solar-like oscillations. These are H-shell-burning stars, whose oscillations should be valuable for testing models of stellar evolution and for constraining the star-formation rate in the local disk. We use a new technique to compare stars on a single echelle diagram by scaling their frequencies and find well-defined ridges corresponding to radial and non-radial oscillations, including clear evidence for modes with angular degree l=3. Measuring the small separation between l=0 and l=2 allows us to plot the so-called C-D diagram of delta nu_02 versus Delta nu. The small separation delta nu_01 of l=1 from the midpoint of adjacent l=0 modes is negative, contrary to the Sun and solar-type stars. The ridge for l=1 is notably broadened, which we attribute to mixed modes, confirming theoretical predictions for low-luminosity giants. Overall, the results demonstrate the tremendous potential of Kepler data for asteroseismology of red giants.

astro-ph.SR↗

arXiv2005

Circular polarization dependent study of the microwave photoconductivity in a two-dimensional electron system

The polarization dependence of the low field microwave photoconductivity and absorption of a two-dimensional electron system has been investigated in a quasi-optical setup in which linear and any circular polarization can be produced in-situ. The microwave induced resistance oscillations and the zero resistance regions are notedly immune to the sense of circular polarization. This observation is discrepant with a number of proposed theories. Deviations only occur near the cyclotron resonance absorption where an unprecedented large resistance response is observed.

cond-mat.mes-hall↗