Extremely high room-temperature two-dimensional hole gas mobility in Ge/Si0.33Ge0.67/Si(001) p-type modulation-doped heterostructures

To extract the room-temperature drift mobility and sheet carrier density of two-dimensional hole gas (2DHG) that form in Ge strained channels of various thicknesses in Ge/Si0.33Ge0.67/Si(001) p-type modulation-doped heterostructures, the magnetic field dependences of the magnetoresistance and Hall resistance at temperature of 295 K were measured and the technique of maximum entropy mobility spectrum analysis was applied. This technique allows a unique determination of mobility and sheet carrier density of each group of carriers present in parallel conducting multilayers semiconductor heterostructures. Extremely high room-temperature drift mobility (at sheet carrier density) of 2DHG 2940 cm2 V–1 s–1 (5.11×1011 cm–2) was obtained in a sample with a 20 nm thick Ge strained channel

Fermi surface and quasiparticle dynamics of Na(x)CoO2 {x=0.7} investigated by Angle-Resolved Photoemission Spectroscopy

We present an angle-resolved photoemission study of Na0.7CoO2, the host cobaltate of the NaxCoO2.yH2O series. Our results show a large hexagonal-like hole-type Fermi surface, an extremely narrow strongly renormalized quasiparticle band and a small Fermi velocity. Along the Gamma to M high symmetry line, the quasiparticle band crosses the Fermi level from M toward Gamma consistent with a negative sign of effective single-particle hopping (t ): t is estimated to be about 8 meV which is on the order of exchange coupling J in this system. This suggests that t ~ J ~ 10 meV is an important energy scale in the system. Quasiparticles are well defined only in the T-linear resistivity regime. Small single particle hopping and unconventional quasiparticle dynamics may have implications for understanding the unusual behavior of this new class of compounds.Comment: Revised text, Added Figs, Submitted to PR

Excited-state optically detected magnetic resonance of spin defects in hexagonal boron nitride

Negatively charged boron vacancy (VB-) centers in hexagonal boron nitride (hBN) are promising spin defects in a van der Waals crystal. Understanding the spin properties of the excited state (ES) is critical for realizing dynamic nuclear polarization. Here, we report zero-field splitting in the ES of DES = 2160 MHz and an optically detected magnetic resonance (ODMR) contrast of 12% at cryogenic temperature. The ES has a g-factor similar to the ground state. The ES photodynamics is further elucidated by measuring the level anti-crossing of the VB- defects under varying external magnetic fields. In contrast to nitrogen vacancy (NV-) centers in diamond, the emission change caused by excited-state level anti-crossing (ESLAC) is more prominent at cryo-temperature than at room temperature. Our results provide important information for utilizing the spin defects of hBN in quantum technology

The Security Blanket of the Chat World: An Analytic Evaluation and a User Study of Telegram

The computer security community has advocated widespread adoption of secure communication tools to protect personal privacy. Several popular communication tools have adopted end-to-end encryption (e.g., WhatsApp, iMessage), or promoted security features as selling points (e.g., Telegram, Signal). However, previous studies have shown that users may not understand the security features of the tools they are using, and may not be using them correctly. In this paper, we present a study of Telegram using two complementary methods: (1) a labbased user study (11 novices and 11 Telegram users), and (2) a hybrid analytical approach combining cognitive walk-through and heuristic evaluation to analyse Telegram’s user interface. Participants who use Telegram feel secure because they feel they are using a secure tool, but in reality Telegram offers limited security benefits to most of its users. Most participants develop a habit of using the less secure default chat mode at all times. We also uncover several user interface design issues that impact security, including technical jargon, inconsistent use of terminology, and making some security features clear and others not. For instance, use of the end-to-end-encrypted Secret Chat mode requires both the sender and recipient be online at the same time, and Secret Chat does not support group conversations

Co-Firing of Spatially Varying Dielectric Ca–Mg–Silicate and Bi–Ba–Nd–Titanate Composite

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/65424/1/j.1551-2916.2005.00498.x.pd

Comparative Energy Analysis of VRF and VAV Systems under Cooling Mode

Archit ectural Engineering at University of Colorado at Boulder, CO, 80309, USA VRF systems are larger capacity more complex versions of ductless multi-split or mini-split heat pump systems. Their design differs from unitary air conditioner systems, which distribute cooled air through ductwork, or chiller systems, which distribute cold water through pipes. Generally, a single compact air-cooled condensing unit located outdoor consists of a variable-speed and a constant-speed compressor, and it is able to link to several numbers of indoor evaporator units. Modular design allows for flexible installation and connection of multiple indoor units of varying configurations and capacities. The VRF system is able to control the refrigerant flow rate to the indoor units individually according to the cooling or heating load of the zone served by each indoor unit. A typical VRF outdoor condensing unit has a cooling capacity of 72,000-192,000 Btu/h, however for buildings that require larger cooling capacities, the VRF system is able to integrate multiple condensing units to serve large air-conditioning loads. Abstract Variable refrigerant flow (VRF) or variable refrigerant volume (VRV) systems provide many benefits over traditional airconditioning systems, with great potential to decrease energy cost and increase thermal comfort in buildings. This paper presents a method to size and select VRF systems and to compute its annual energy consumption. The study compares the cooling energy usage of a VRF system against a conventional chiller-based variable-air-volume (VAV) system and a packaged VAV (PVAV) system for a typical light commercial building. The results reveal that the peak electrical demand of the VRF system for the cooling season is about 60% of the chiller-based VAV system and 70% of the packaged VAV systems, and the operating energy usage is about 53% of the chiller-based VAV system and 60% of the packaged VAV system for the building studied

Relative contributions of the logging, fiber, oil palm, and mining industries to forest loss in Indonesia

Article first published online: 21 APR 2014Indonesia contributes significantly to deforestation in Southeast Asia. However, much uncertainty remains over the relative contributions of various forest-exploiting sectors to forest losses in the country. Here, we compare the magnitudes of forest and carbon loss, and forest and carbon stocks remaining within oil palm plantation, logging, fiber plantation (pulp and paper), and coal mining concessions in Indonesia. Forest loss in all industrial concessions, including logging concessions, relate to the conversion of forest to nonforest land cover. We found that the four industries accounted for ∼44.7% (∼6.6 Mha) of forest loss in Kalimantan, Sumatra, Papua, Sulawesi, and Moluccas between 2000 and 2010. Fiber plantation and logging concessions accounted for the largest forest loss (∼1.9 Mha and ∼1.8 Mha, respectively). Although the oil palm industry is often highlighted as a major driver of deforestation, it was ranked third in terms of deforestation (∼1 Mha), and second in terms of carbon dioxide emissions (∼1,300–2,350 Mt CO2). Crucially, ∼34.6% (∼26.8 Mha) of Indonesia's remaining forests is located within industrial concessions, the majority of which is found within logging concessions (∼18.8 Mha). Hence, future development plans within Indonesia's industrial sectors weigh heavily on the fate of Southeast Asia's remaining forests and carbon stocks.Sinan A. Abood, Janice Ser Huay Lee, Zuzana Burivalova, John Garcia-Ulloa, and Lian Pin Ko