14,379 research outputs found
Analytical models of power losses of a three phase AC-DC rectifier for hybrid electric vehicles
This paper presents the investigation of analytical models for the approximation of conduction and switching losses of the power-switch network in a three-phase AC-DC matrix rectifier. Analytical models of conduction and switching losses can provide circuit designers with a measurable way to approximate the total losses of the given power converter at different operating points so as to estimate the trend of the loss versus the change of the operating points
The properties of active galaxies at the extreme of eigenvector 1
Eigenvector 1 (EV1) is the formal parameter which allows the introduction of
some order in the properties of the unobscured type 1 active galaxies. We aim
to understand the nature of this parameter by analyzing the most extreme
examples of quasars with the highest possible values of the corresponding
eigenvalues . We selected the appropriate sources from the Sloan
Digital Sky Survey (SDSS) and performed detailed modeling, including various
templates for the Fe II pseudo-continuum and the starlight contribution to the
spectrum. Out of 27 sources with larger than 1.3 and with the
measurement errors smaller than 20\% selected from the SDSS quasar catalog,
only six sources were confirmed to have a high value of , defined as
being above 1.3. All other sources have of approximately 1. Three
of the high objects have a very narrow H line, below 2100 km
s but three sources have broad lines, above 4500 km s, that do
not seem to form a uniform group, differing considerably in black hole mass and
Eddington ratio; they simply have a very similar EW([OIII]5007) line.
Therefore, the interpretation of the EV1 remains an open issue.Comment: Astronomy and Astrophysics (in press
Small business resilience in a remote tourist destination: exploring close relationship capabilities on the Island of St Helena
We investigate how small businesses in a very remote island tourist destination are able to cope with shocks and disruptions they face, that is, their resilience. Given their size and resource limitations as well as disadvantages due to lack of accessibility and remoteness, we expect resilience in these types of firms to be underpinned by their close relationships with other local stakeholders. Drawing on concepts from Instrumental Stakeholder Theory (IST), we explore how close relationship capabilities with stakeholders affect small business resilience on the remote tourist destination of St Helena. Through in-depth interviews with the owner-managers of seven case firms on the island we identify how aspects of IST are relevant to resilience, while also uncovering emerging variables of interest. To make sense of these variables we use a Fuzzy Cognitive Mapping (FCM) approach, capturing respondentsâ mental models in graphical form. The result supports IST by reinforcing the positive effects of valuable partners and mutually beneficial interaction with valuable partners, as well as a negative impact of the cost of managing relationships. However, negative impacts of logistical costs and, surprisingly, the role of government policy on resilience are also identified. Implications for research and policy are discussed
The unique rapid variabilities of the iron K line profiles in NGC 4151
We present a detailed analysis of the iron K line variabilities in
NGC 4151 by using long ASCA observation data obtained in May 1995. Despite the
relatively small amplitude variations in the continuum flux, the iron K
line flux and profile show dramatic variations. Particularly, the line profile
changes from single peak to seeming double peaks and back in time scales of a
few 10 sec. The seemingly double-peaked profiles can be well interpreted as
line emission from a Keplerian ring around a massive black hole. An absorption
line at around 5.9 keV is also marginnaly detected. We discussed current Fe K
line models, but none of them can well explain the observed line and continuum
variations.Comment: 18 pages, latex, 3 figures, ApJ accepte
Fault diagnostic instrumentation design for environmental control and life support systems
As a development phase moves toward flight hardware, the system availability becomes an important design aspect which requires high reliability and maintainability. As part of continous development efforts, a program to evaluate, design, and demonstrate advanced instrumentation fault diagnostics was successfully completed. Fault tolerance designs for reliability and other instrumenation capabilities to increase maintainability were evaluated and studied
Cooling a mechanical resonator via coupling to a tunable double quantum dot
We study the cooling of a mechanical resonator (MR) that is capacitively
coupled to a double quantum dot (DQD). The MR is cooled by the dynamical
backaction induced by the capacitive coupling between the DQD and the MR. The
DQD is excited by a microwave field and afterwards a tunneling event results in
the decay of the excited state of the DQD. An important advantage of this
system is that both the energy level splitting and the decay rate of the DQD
can be well tuned by varying the gate voltage. We find that the steady average
occupancy, below unity, of the MR can be achieved by changing both the decay
rate of the excited state and the detuning between the transition frequency of
the DQD and the microwave frequency, in analogy to the laser sideband cooling
of an atom or trapped ion in atomic physics. Our results show that the cooling
of the MR to the ground state is experimentally implementable.Comment: 10 pages, 5 figure
Probing tiny motions of nanomechanical resonators: classical or quantum mechanical?
We propose a spectroscopic approach to probe tiny vibrations of a
nanomechanical resonator (NAMR), which may reveal classical or quantum behavior
depending on the decoherence-inducing environment. Our proposal is based on the
detection of the voltage-fluctuation spectrum in a superconducting transmission
line resonator (TLR), which is {\it indirectly} coupled to the NAMR via a
controllable Josephson qubit acting as a quantum transducer. The classical
(quantum mechanical) vibrations of the NAMR induce symmetric (asymmetric) Stark
shifts of the qubit levels, which can be measured by the voltage fluctuations
in the TLR. Thus, the motion of the NAMR, including if it is quantum mechanical
or not, could be probed by detecting the voltage-fluctuation spectrum of the
TLR.Comment: 4 pages, 3 figures. to appear in Physical Review Letter
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