184,446 research outputs found
Overall properties of the Gaia DR1 reference frame
We compare quasar positions of the auxiliary quasar solution with ICRF2
sources using different samples and evaluate the influence on the {\it Gaia}
DR1 reference frame owing to the Galactic aberration effect over the
J2000.0-J20015.0 period. Then we estimate the global rotation between TGAS with
{\it Tycho}-2 proper motion systems to investigate the property of the {\it
Gaia} DR1 reference frame. Finally, the Galactic kinematics analysis using the
K-M giant proper motions is performed to understand the property of {\it Gaia}
DR1 reference frame. The positional comparison between the auxiliary quasar
solution and ICRF2 shows negligible orientation and validates the declination
bias of \mas~in {\it Gaia} quasar positions with respect to ICRF2.
Galactic aberration effect is thought to cause an offset \mas~of
the axis direction of {\it Gaia} DR1 reference frame. The global rotation
between TGAS and {\it Tycho}-2 proper motion systems, obtained by different
samples, shows a much smaller value than the claimed value \masyr. For
the Galactic kinematics analysis of the TGAS K-M giants, we find possible
non-zero Galactic rotation components beyond the classical Oort constants: the
rigid part \masyr~and the differential part
\masyr~around the axis of Galactic
coordinates, which indicates possible residual rotation in {\it Gaia} DR1
reference frame or problems in the current Galactic kinematical model.Comment: 6 pages, 1 figure. Accepted for publication in A&
Comparative study of commercial building energy-efficiency retrofit policies in four pilot cities in China
The energy efficiency of existing commercial buildings is more challenging to regulate and improve than the energy efficiency of new constructions. In 2011 and 2012, the Chinese Government selected four cities- Shanghai, Tianjin, Shenzhen, and Chongqing- to implement pilot commercial building energy efficiency retrofit program. Based on site surveys and expert interviews in these pilot cities, this research conducted a comparative analysis on incentive policies of local city level. The analysis results show that policy designs of existing commercial buildings should be further improved. The aspects that influence the implementation effect in the future, such as subsidy level, installments, and business model promotion, should be specified in the policy clauses. Referring to the technical solution and cost-benefit in Chongqing, we found that lighting system is the most common retrofit objects while envelope system is the least common one. And the subsidy incentive is greatest for educational buildings, followed by office buildings. In the end, we further discussed the problems and obstacles in commercial building retrofit market, and provided a series of recommendations
Phase Diffusion in Single-Walled Carbon Nanotube Josephson Transistors
We investigate electronic transport in Josephson junctions formed by
single-walled carbon nanotubes coupled to superconducting electrodes. We
observe enhanced zero-bias conductance (up to 10e^2/h) and pronounced
sub-harmonic gap structures in differential conductance, which arise from the
multiple Andreev reflections at superconductor/nanotube interfaces. The
voltage-current characteristics of these junctions display abrupt switching
from the supercurrent branch to resistive branch, with a gate-tunable switching
current ranging from 50 pA to 2.3 nA. The finite resistance observed on the
supercurrent branch and the magnitude of the switching current are in good
agreement with calculation based on the model of classical phase diffusion
Detection of a new methanol maser line with ALMA
Aims. We aimed at investigating the structure and kinematics of the gaseous
disk and outflows around the massive YSO S255 NIRS3 in the S255IR-SMA1 dense
clump. Methods. Observations of the S255IR region were carried out with ALMA at
two epochs in the compact and extended configurations. Results. We
serendipitously detected a new, never predicted, bright maser line at about
349.1 GHz, which most probably represents the CHOH A transition. The emission covers most of the 6.7 GHz methanol maser emission
area of almost 1 in size and shows a velocity gradient in the
same sense as the disk rotation. No variability was found on the time interval
of several months. It is classified as Class II maser and probably originates
in a ring at a distance of several hundreds AU from the central star.Comment: 4 pages, 4 figures, accepted by Astronomy and Astrophysic
Zero Modes of Matter Fields on Scalar Flat Thick Branes
Zero modes of various matters with spin 0, 1 and 1/2 on a class of scalar
flat thick branes are discussed in this paper. We show that scalar field with
spin 0 is localized on all thick branes without additional condition, while
spin 1 vector field is not localized. In addition, for spin 1/2 fermionic
field, the zero mode is localized on the branes under certain conditions.Comment: 11 pages,no figure
On Ladder Logic Bombs in Industrial Control Systems
In industrial control systems, devices such as Programmable Logic Controllers
(PLCs) are commonly used to directly interact with sensors and actuators, and
perform local automatic control. PLCs run software on two different layers: a)
firmware (i.e. the OS) and b) control logic (processing sensor readings to
determine control actions). In this work, we discuss ladder logic bombs, i.e.
malware written in ladder logic (or one of the other IEC 61131-3-compatible
languages). Such malware would be inserted by an attacker into existing control
logic on a PLC, and either persistently change the behavior, or wait for
specific trigger signals to activate malicious behaviour. For example, the LLB
could replace legitimate sensor readings with manipulated values. We see the
concept of LLBs as a generalization of attacks such as the Stuxnet attack. We
introduce LLBs on an abstract level, and then demonstrate several designs based
on real PLC devices in our lab. In particular, we also focus on stealthy LLBs,
i.e. LLBs that are hard to detect by human operators manually validating the
program running in PLCs. In addition to introducing vulnerabilities on the
logic layer, we also discuss countermeasures and we propose two detection
techniques.Comment: 11 pages, 14 figures, 2 tables, 1 algorith
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