Variable-speed tail rotors for helicopters with variable-speed main rotors

Variable tail rotor speed is investigated as a method for reducing tail rotor power, and improving helicopter performance. A helicopter model able to predict the main rotor and tail rotor powers is presented, and the flight test data of the UH-60A helicopter is used for validation. The predictions of the main and tail rotor powers are generally in good agreement with flight tests, which justifies the use of the present method in analyzing main and tail rotors. Reducing the main rotor speed can result in lower main rotor power at certain flight conditions. However, it increases the main rotor torque and the corresponding required tail rotor thrust to trim, which then decreases the yaw control margin of the tail rotor. In hover, the tail rotor may not be able to provide enough thrust to counter the main rotor torque, if it is slowed to follow the main rotor speed. The main rotor speed corresponding to the minimum main rotor power increases, if the change of tail rotor power in hover is considered. As a helicopter translated to cruise, the induced power decreases, and the profile power increases, with the profile power dominating the tail rotor. Reducing the tail rotor speed in cruise reduces the profile power to give a 37% reduction in total tail rotor power and a 1.4% reduction to total helicopter power. In high speed flight, varying the tail rotor speed is ineffective for power reduction. The power reduction obtained by the variable tail rotor speed is reduced for increased helicopter weight

A Fast Blind Impulse Detector for Bernoulli-Gaussian Noise in Underspread Channel

The Bernoulli-Gaussian (BG) model is practical to characterize impulsive noises that widely exist in various communication systems. To estimate the BG model parameters from noise measurements, a precise impulse detection is essential. In this paper, we propose a novel blind impulse detector, which is proven to be fast and accurate for BG noise in underspread communication channels.Comment: v2 to appear in IEEE ICC 2018, Kansas City, MO, USA, May 2018 Minor erratums added in v

MoS2 Dual-Gate MOSFET with Atomic-Layer-Deposited Al2O3 as Top-Gate Dielectric

We demonstrate atomic-layer-deposited (ALD) high-k dielectric integration on two-dimensional (2D) layer-structured molybdenum disulfide (MoS2) crystals and MoS2 dual-gate n-channel MOSFETs with ALD Al2O3 as top-gate dielectric. Our C-V study of MOSFET structures shows good interface between 2D MoS2 crystal and ALD Al2O3. Maximum drain currents using back-gates and top-gates are measured to be 7.07mA/mm and 6.42mA/mm at Vds=2V with a channel width of 3 {\mu}m, a channel length of 9 {\mu}m, and a top-gate length of 3 {\mu}m. We achieve the highest field-effect mobility of electrons using back-gate control to be 517 cm^2/Vs. The highest current on/off ratio is over 10^8.Comment: submitted to IEEE Electron Device Letter

FGGE/SMMR-30 tape specification and shipping letter description

The Nimbus-7 FGGE/SMMR-30 tape which contains sea ice concentration data in 30 km resolution which are extracted and reformatted from Nimbus-7 SMMR PARM-30 tapes in accordance with the FGGE level II International Exchange Format Specification is outlined. There are three types of files on a FGGE/SMMR-30 tape. The first file on the tape is a test file. The second file on the tape is a tape header file. The remaining one or more files are data files. All files are terminated with a single end of file (EOP) tape mark. The last file is terminated with two EOF tape marks. All files are made up of one or more physical records. Each physical record contains 2960 bytes. Each data file contains all available values for a 6 hour synoptic time period

Criticality and Continuity of Explosive Site Percolation in Random Networks

This Letter studies the critical point as well as the discontinuity of a class of explosive site percolation in Erd\"{o}s and R\'{e}nyi (ER) random network. The class of the percolation is implemented by introducing a best-of-m rule. Two major results are found: i). For any specific $m$, the critical percolation point scales with the average degree of the network while its exponent associated with $m$ is bounded by -1 and $\sim-0.5$. ii). Discontinuous percolation could occur on sparse networks if and only if $m$ approaches infinite. These results not only generalize some conclusions of ordinary percolation but also provide new insights to the network robustness.Comment: 5 pages, 5 figure

Drell-Yan plus missing energy as a signal for extra dimensions

We explore the search sensitivity for signals of large extra dimensions at hadron colliders via the Drell-Yan process pp -> l+ l- + E_T(miss) X (l = e,mu) where the missing transverse energy is the result of escaping Kaluza-Klein gravitons. We find that one is able to place exclusion limits on the gravity scale up to 560 GeV at the Fermilab Tevatron, and to 4.0 (3.3) TeV at the CERN LHC, for n = 3 (4) extra dimensions.Comment: 5 pages, 2 PS figs, revised verseion to be published in Physics Letters

TeV resonances in top physics at the LHC

We consider the possibility of studying novel particles at the TeV scale with enhanced couplings to the top quark via top quark pair production at the LHC and VLHC. In particular we discuss the case of neutral scalar and vector resonances associated with a strongly interacting electroweak symmetry breaking sector. We constrain the couplings of these resonances by imposing appropriate partial wave unitarity conditions and known low energy constraints. We evaluate the new physics signals via WW -> tt~ for various models without making approximation for the initial state W bosons, and optimize the acceptance cuts for the signal observation. We conclude that QCD backgrounds overwhelm the signals in both the LHC and a 200 TeV VLHC, making it impossible to study this type of physics in the tt~ channel at those machines.Comment: 15p, add. comments to clarify model, +2 ref., version to appear PR