48,568 research outputs found
Is There a Market for Work Group Servers? Evaluating Market Level Demand Elasticities Using Micro and Macro Models
This paper contains an empirical analysis demand for "work-group" (or low-end) servers. Servers are at thecentre of many US and EU anti-trust debates, including the Hewlett-Packard/Compaq merger and investigationsinto the activities of Microsoft. One question in these policy decisions is whether a high share of work serversindicates anything about shortrun market power. To investigate price elasticities we use model-level panel dataon transaction prices, sales and characteristics of practically every server in the world. We contrast estimatesfrom the traditional "macro" approaches that aggregate across brands and modern "micro" approaches that usebrand-level information (including both "distance metric" and logit based approaches). We find that the macroapproaches lead to overestimates of consumer price sensitivity. Our preferred micro-based estimates of themarket level elasticity of demand for work group servers are around 0.3 to 0.6 (compared to 1 to 1.3 in themacro estimates). Even at the higher range of the estimates, however, we find that demand elasticities aresufficiently low to imply a distinct "anti-trust" market for work group servers and their operating systems. It isunsurprising that firms with large shares of work group servers have come under some antitrust scrutiny.demand elasticities, network servers, computers, anti-trust
Building the Evryscope: Hardware Design and Performance
The Evryscope is a telescope array designed to open a new parameter space in
optical astronomy, detecting short timescale events across extremely large sky
areas simultaneously. The system consists of a 780 MPix 22-camera array with an
8150 sq. deg. field of view, 13" per pixel sampling, and the ability to detect
objects down to Mg=16 in each 2 minute dark-sky exposure. The Evryscope,
covering 18,400 sq.deg. with hours of high-cadence exposure time each night, is
designed to find the rare events that require all-sky monitoring, including
transiting exoplanets around exotic stars like white dwarfs and hot subdwarfs,
stellar activity of all types within our galaxy, nearby supernovae, and other
transient events such as gamma ray bursts and gravitational-wave
electromagnetic counterparts. The system averages 5000 images per night with
~300,000 sources per image, and to date has taken over 3.0M images, totaling
250TB of raw data. The resulting light curve database has light curves for 9.3M
targets, averaging 32,600 epochs per target through 2018. This paper summarizes
the hardware and performance of the Evryscope, including the lessons learned
during telescope design, electronics design, a procedure for the precision
polar alignment of mounts for Evryscope-like systems, robotic control and
operations, and safety and performance-optimization systems. We measure the
on-sky performance of the Evryscope, discuss its data-analysis pipelines, and
present some example variable star and eclipsing binary discoveries from the
telescope. We also discuss new discoveries of very rare objects including 2 hot
subdwarf eclipsing binaries with late M-dwarf secondaries (HW Vir systems), 2
white dwarf / hot subdwarf short-period binaries, and 4 hot subdwarf reflection
binaries. We conclude with the status of our transit surveys, M-dwarf flare
survey, and transient detection.Comment: 24 pages, 24 figures, accepted PAS
Understanding the fine structure of electricity prices
This paper analyzes the special features of electricity spot prices derived from the physics of this commodity and from the economics of supply and demand in a market pool. Besides mean reversion, a property they share with other commodities, power prices exhibit the unique feature of spikes in trajectories. We introduce a class of discontinuous processes exhibiting a "jump-reversion" component to properly represent these sharp upward moves shortly followed by drops of similar magnitude. Our approach allows to capture—for the first time to our knowledge—both the trajectorial and the statistical properties of electricity pool prices. The quality of the fitting is illustrated on a database of major U.S. power markets
Schottky mass measurements of heavy neutron-rich nuclides in the element range 70\leZ \le79 at the ESR
Storage-ring mass spectrometry was applied to neutron-rich Au
projectile fragments. Masses of Lu, Hf, Ta,
W, and Re nuclei were measured for the first time. The
uncertainty of previously known masses of W and Os nuclei
was improved. Observed irregularities on the smooth two-neutron separation
energies for Hf and W isotopes are linked to the collectivity phenomena in the
corresponding nuclei.Comment: 10 pages, 9 figures, 2 table
Solar Orbiter: Exploring the Sun-heliosphere connection
The heliosphere represents a uniquely accessible domain of space, where
fundamental physical processes common to solar, astrophysical and laboratory
plasmas can be studied under conditions impossible to reproduce on Earth and
unfeasible to observe from astronomical distances. Solar Orbiter, the first
mission of ESA's Cosmic Vision 2015-2025 programme, will address the central
question of heliophysics: How does the Sun create and control the heliosphere?
In this paper, we present the scientific goals of the mission and provide an
overview of the mission implementation.Comment: 52 pages, 21 figures, 125 references; accepted for publication in
Solar Physic
System configuration, fault detection, location, isolation and restoration: a review on LVDC Microgrid protections
Low voltage direct current (LVDC) distribution has gained the significant interest of research due to the advancements in power conversion technologies. However, the use of converters has given rise to several technical issues regarding their protections and controls of such devices under faulty conditions. Post-fault behaviour of converter-fed LVDC system involves both active converter control and passive circuit transient of similar time scale, which makes the protection for LVDC distribution significantly different and more challenging than low voltage AC. These protection and operational issues have handicapped the practical applications of DC distribution. This paper presents state-of-the-art protection schemes developed for DC Microgrids. With a close look at practical limitations such as the dependency on modelling accuracy, requirement on communications and so forth, a comprehensive evaluation is carried out on those system approaches in terms of system configurations, fault detection, location, isolation and restoration
The Pan-STARRS Moving Object Processing System
We describe the Pan-STARRS Moving Object Processing System (MOPS), a modern
software package that produces automatic asteroid discoveries and
identifications from catalogs of transient detections from next-generation
astronomical survey telescopes. MOPS achieves > 99.5% efficiency in producing
orbits from a synthetic but realistic population of asteroids whose
measurements were simulated for a Pan-STARRS4-class telescope. Additionally,
using a non-physical grid population, we demonstrate that MOPS can detect
populations of currently unknown objects such as interstellar asteroids.
MOPS has been adapted successfully to the prototype Pan-STARRS1 telescope
despite differences in expected false detection rates, fill-factor loss and
relatively sparse observing cadence compared to a hypothetical Pan-STARRS4
telescope and survey. MOPS remains >99.5% efficient at detecting objects on a
single night but drops to 80% efficiency at producing orbits for objects
detected on multiple nights. This loss is primarily due to configurable MOPS
processing limits that are not yet tuned for the Pan-STARRS1 mission.
The core MOPS software package is the product of more than 15 person-years of
software development and incorporates countless additional years of effort in
third-party software to perform lower-level functions such as spatial searching
or orbit determination. We describe the high-level design of MOPS and essential
subcomponents, the suitability of MOPS for other survey programs, and suggest a
road map for future MOPS development.Comment: 57 Pages, 26 Figures, 13 Table
MAX 1991. The active sun: A plan for pursuing the study of the active sun at the time of the next maximum in solar activity, January 1985
The results of the discusions of a working group for the definition of a program for the forthcoming crest of solar activity, 1990 to 1993 are presented. The MAX '91 program described are intended to achieve important scientific goals within the context of the natural solar variability. The heart of the MAX '91 program is a series of campaigns oriented towards specific scientific problems, and taking place in the solar maximum period 1990 to 1993. These campaigns will take advantage of the load-carrying capability of the Space Shuttle to fly instruments with observational capabilities very different from those of the Solar Maximum Mission. Various combinations of instruments appropriate to the specific scientific problem of a given campaign would be flown on a Shuttle sortie mission
Germin and germin-like proteins: evolution, structure, and function
Germin and germin-like proteins (GLPs) are encoded by a family of genes found in all plants. They are part of the cupin superfamily of biochemically diverse proteins, a superfamily that has a conserved tertiary structure, though with limited similarity in primary sequence. The subgroups of GLPs have different enzyme functions that include the two hydrogen peroxide-generating enzymes, oxalate oxidase (OxO) and superoxide dismutase. This review summarizes the sequence and structural details of GLPs and also discusses their evolutionary progression, particularly their amplification in gene number during the evolution of the land plants. In terms of function, the GLPs are known to be differentially expressed during specific periods of plant growth and development, a pattern of evolutionary subfunctionalization. They are also implicated in the response of plants to biotic (viruses, bacteria, mycorrhizae, fungi, insects, nematodes, and parasitic plants) and abiotic (salt, heat/cold, drought, nutrient, and metal) stress. Most detailed data come from studies of fungal pathogenesis in cereals. This involvement with the protection of plants from environmental stress of various types has led to numerous plant breeding studies that have found links between GLPs and QTLs for disease and stress resistance. In addition the OxO enzyme has considerable commercial significance, based principally on its use in the medical diagnosis of oxalate concentration in plasma and urine. Finally, this review provides information on the nutritional importance of these proteins in the human diet, as several members are known to be allergenic, a feature related to their thermal stability and evolutionary connection to the seed storage proteins, also members of the cupin superfamily
Design of adaptive analog filters for magnetic front-end read channels
Esta tese estuda o projecto e o comportamento de filtros em tempo contínuo de
muito-alta-frequência. A motivação deste trabalho foi a investigação de soluções de filtragem
para canais de leitura em sistemas de gravação e reprodução de dados em suporte
magnético, com custos e consumo (tamanho total inferior a 1 mm2 e consumo inferior a
1mW/polo), inferiores aos circuitos existentes. Nesse sentido, tal como foi feito neste
trabalho, o rápido desenvolvimento das tecnologias de microelectrónica suscitou esforços
muito significativos a nível mundial com o objectivo de se investigarem novas técnicas
de realização de filtros em circuito integrado monolítico, especialmente em tecnologia
CMOS (Complementary Metal Oxide Semiconductor). Apresenta-se um estudo comparativo
a diversos níveis hierárquicos do projecto, que conduziu à realização e caracterização
de soluções com as características desejadas.
Num primeiro nível, este estudo aborda a questão conceptual da gravação e transmissão
de sinal bem como a escolha de bons modelos matemáticos para o tratamento da
informação e a minimização de erro inerente às aproximações na conformidade aos princípios
físicos dos dispositivos caracterizados.
O trabalho principal da tese é focado nos níveis hierárquicos da arquitectura do
canal de leitura e da realização em circuito integrado do seu bloco principal – o bloco de
filtragem. Ao nível da arquitectura do canal de leitura, apresenta-se um estudo alargado
sobre as metodologias existentes de adaptação de sinal e recuperação de dados em suporte
magnético. Este desígnio aparece no âmbito da proposta de uma solução de baixo custo,
baixo consumo, baixa tensão de alimentação e baixa complexidade, alicerçada em tecnologia
digital CMOS, para a realização de um sistema DFE (Decision Feedback Equalization)
com base na igualização de sinal utilizando filtros integrados analógicos em tempo
contínuo.
Ao nível do projecto de realização do bloco de filtragem e das técnicas de implementação
de filtros e dos seus blocos constituintes em circuito integrado, concluiu-se que
a técnica baseada em circuitos de transcondutância e condensadores, também conhecida como filtros gm-C (ou transcondutância-C), é a mais adequada para a realização de filtros
adaptativos em muito-alta-frequência. Definiram-se neste nível hierárquico mais baixo,
dois subníveis de aprofundamento do estudo no âmbito desta tese, nomeadamente: a pesquisa
e análise de estruturas ideais no projecto de filtros recorrendo a representações no
espaço de estados; e, o estudo de técnicas de realização em tecnologia digital CMOS de
circuitos de transcondutância para a implementação de filtros integrados analógicos em
tempo contínuo.
Na sequência deste estudo, apresentam-se e comparam-se duas estruturas de filtros
no espaço de estados, correspondentes a duas soluções alternativas para a realização de
um igualador adaptativo realizado por um filtro contínuo passa-tudo de terceira ordem,
para utilização num canal de leitura de dados em suporte magnético.
Como parte constituinte destes filtros, apresenta-se uma técnica de realização de
circuitos de transcondutância, e de realização de condensadores lineares usando matrizes
de transístores MOSFET para processamento de sinal em muito-alta-frequência realizada
em circuito integrado usando tecnologia digital CMOS submicrométrica. Apresentam-se
métodos de adaptação automática capazes de compensar os erros face aos valores nominais
dos componentes, devidos às tolerâncias inerentes ao processo de fabrico, para os
quais apresentamos os resultados de simulação e de medição experimental obtidos.
Na sequência deste estudo, resultou igualmente a apresentação de um circuito passível
de constituir uma solução para o controlo de posicionamento da cabeça de leitura
em sistemas de gravação/reprodução de dados em suporte magnético. O bloco proposto
é um filtro adaptativo de primeira ordem, com base nos mesmos circuitos de transcondutância
e técnicas de igualação propostos e utilizados na implementação do filtro adaptativo
de igualação do canal de leitura.
Este bloco de filtragem foi projectado e incluído num circuito integrado (Jaguar) de
controlo de posicionamento da cabeça de leitura realizado para a empresa ATMEL em
Colorado Springs, e incluído num produto comercial em parceria com uma empresa escocesa
utilizado em discos rígidos amovíveis.This thesis studies the design and behavior of continuous-time very-high-frequency
filters. The motivation of this work was the search for filtering solutions for the readchannel
in recording and reproduction of data on magnetic media systems, with costs and
consumption (total size less than 1 mm2 and consumption under 1mW/pole), lower than
the available circuits. Accordingly, as was done in this work, the rapid development of
microelectronics technology raised very significant efforts worldwide in order to investigate
new techniques for implementing such filters in monolithic integrated circuit, especially
in CMOS technology (Complementary Metal Oxide Semiconductor). We present
a comparative study on different hierarchical levels of the project, which led to the realization
and characterization of solutions with the desired characteristics.
In the first level, this study addresses the conceptual question of recording and
transmission of signal and the choice of good mathematical models for the processing of
information and minimization of error inherent in the approaches and in accordance with
the principles of the characterized physical devices.
The main work of this thesis is focused on the hierarchical levels of the architecture
of the read channel and the integrated circuit implementation of its main block - the filtering
block. At the architecture level of the read channel this work presents a comprehensive
study on existing methodologies of adaptation and signal recovery of data on
magnetic media. This project appears in the sequence of the proposed solution for a lowcost,
low consumption, low voltage, low complexity, using CMOS digital technology for
the performance of a DFE (Decision Feedback Equalization) based on the equalization of
the signal using integrated analog filters in continuous time.
At the project level of implementation of the filtering block and techniques for implementing
filters and its building components, it was concluded that the technique based
on transconductance circuits and capacitors, also known as gm-C filters is the most appropriate
for the implementation of very-high-frequency adaptive filters. We defined in
this lower level, two sub-levels of depth study for this thesis, namely: research and analysis
of optimal structures for the design of state-space filters, and the study of techniques for the design of transconductance cells in digital CMOS circuits for the implementation
of continuous time integrated analog filters.
Following this study, we present and compare two filtering structures operating in
the space of states, corresponding to two alternatives for achieving a realization of an
adaptive equalizer by the use of a continuous-time third order allpass filter, as part of a
read-channel for magnetic media devices.
As a constituent part of these filters, we present a technique for the realization of
transconductance circuits and for the implementation of linear capacitors using arrays of
MOSFET transistors for signal processing in very-high-frequency integrated circuits using
sub-micrometric CMOS technology. We present methods capable of automatic adjustment
and compensation for deviation errors in respect to the nominal values of the
components inherent to the tolerances of the fabrication process, for which we present
the simulation and experimental measurement results obtained.
Also as a result of this study, is the presentation of a circuit that provides a solution
for the control of the head positioning on recording/playback systems of data on magnetic
media. The proposed block is an adaptive first-order filter, based on the same transconductance
circuits and equalization techniques proposed and used in the implementation
of the adaptive filter for the equalization of the read channel.
This filter was designed and included in an integrated circuit (Jaguar) used to control
the positioning of the read-head done for ATMEL company in Colorado Springs, and
part of a commercial product used in removable hard drives fabricated in partnership with a Scottish company
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