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21.
Scientific
activity has been increasing in Puerto Rico in recent years, a development
mirrored not only by the amount of papers published, but by the international
links established for scientific co-operation. The purpose of the present study
is to identify and discuss the patterns of such co-operation, along with the
trends in scientific research conducted in that context at Puerto Rican
institutions. The methodology includes an analysis of the main areas of
research addressed, defined as the area of specialization of the journals
publishing papers indexed in the Science Citation Index (CD-ROM version) from
1980 to 1999. A total of 7271 studies, appearing in 1240 scientific journals,
were selected to study the co-operation established between Puerto Rican institutions
and organizations in other countries. The findings showed a high rate of
international co-operation: 46.07% of the papers published were co-authored by
researchers from other countries. The country accounting for the highest
percentage of joint research was the USA, followed by Germany, United Kingdom,
Canada and Italy. The close relationship between the Puerto Rican and US
scientific systems is not unusual, inasmuch as the economic and socio-political
bonds between them play an essential role in Puerto Rican scientific activity.
The results also revealed substantial differences between the nineteen eighties
and the nineties in terms of the nature of the links established, as well as
growing internationalization of scientific research conducted on the island
over the twenty-year period studied. 相似文献
22.
We consider selfish routing over a network consisting of m parallel
links through which $n$ selfish users route their traffic trying to
minimize their own expected latency. We study the class of mixed
strategies in which the expected latency through each link is at most
a constant multiple of the optimum maximum latency had global
regulation been available. For the case of uniform links it is known
that all Nash equilibria belong to this class of strategies. We are
interested in bounding the coordination ratio (or price of anarchy) of
these strategies defined as the worst-case ratio of the maximum (over
all links) expected latency over the optimum maximum latency. The load
balancing aspect of the problem immediately implies a lower bound
Ω(ln m ln ln m) of the coordination
ratio. We give a tight (up to a multiplicative constant) upper bound.
To show the upper bound, we analyze a variant of the classical balls
and bins problem, in which balls with arbitrary weights are placed
into bins according to arbitrary probability distributions. At the
heart of our approach is a new probabilistic tool that we call ball
fusion; this tool is used to reduce the variant of the problem where
balls bear weights to the classical version (with no weights). Ball
fusion applies to more general settings such as links with arbitrary
capacities and other latency functions. 相似文献
23.
The existence of spectro-temporal receptive fields and evidence for population coding in auditory cortex motivate the development
of such models, that explicitly operate in the time-frequency domain and are based on a pulsed neural network. In presenting
such a model, a formal connection of the fields of Time Frequency Analysis and Pulsed Neural Networks is established. The
resulting neural time-frequency signal representation is shown to be representable as a signal-dependent overcomplete dictionary.
It is derived from neural population coding. Signal decomposition and filtering effects are presented, indicating obvious
technical applications of the proposed model.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
24.
Aldri L. dos Santos Elias P. Duarte Jr. Glenn M. Keeni 《Journal of Network and Systems Management》2004,12(2):191-213
This paper presents a new clustering architecture for SNMP agents that supports semi-active replication of managed objects. A cluster of agents provides fault-tolerant object functionality: replicated managed objects of a crashed agent of a given cluster may be accessed through a peer cluster. The proposed architecture is structured in three layers. The lower layer corresponds to the managed objects at the network elements. The middle layer contains management entities called clusters that monitor and replicate managed objects. The upper layer allows the definition of management clusters as well as the relationship between clusters. A practical tool was implemented and is presented. The impact of replication on network performance is evaluated as well as a probabilistic analysis of replicated object consistency. 相似文献
25.
Zilla Sinuany-Stern Nachum Finger Elias Kligler 《Computers, Environment and Urban Systems》1986,11(4)
This paper provides a model for finding the optimal thinning policy in a pine forest (Pinus halepensis) in Israel. The model simulates the growth of a pine forest stand for timber, under various thinning policies. The annual growth functions are estimated via polynomial regression analysis. The dependent variable is the timber volume of the stand and the explanatory variable is the mean growing space per tree over time. The observations were made over the life span of five experimental parcels in a pine forest in Israel. 相似文献
26.
Jake D. Mehew Selim Unal Elias Torres Alonso Gareth F. Jones Saad Fadhil Ramadhan Monica F. Craciun Saverio Russo 《Advanced materials (Deerfield Beach, Fla.)》2017,29(23)
The combination of graphene with semiconductor materials in heterostructure photodetectors enables amplified detection of femtowatt light signals using micrometer‐scale electronic devices. Presently, long‐lived charge traps limit the speed of such detectors, and impractical strategies, e.g., the use of large gate‐voltage pulses, have been employed to achieve bandwidths suitable for applications such as video‐frame‐rate imaging. Here, atomically thin graphene–WS2 heterostructure photodetectors encapsulated in an ionic polymer are reported, which are uniquely able to operate at bandwidths up to 1.5 kHz whilst maintaining internal gain as large as 106. Highly mobile ions and the nanometer‐scale Debye length of the ionic polymer are used to screen charge traps and tune the Fermi level of the graphene over an unprecedented range at the interface with WS2. Responsivity R = 106 A W?1 and detectivity D* = 3.8 × 1011 Jones are observed, approaching that of single‐photon counters. The combination of both high responsivity and fast response times makes these photodetectors suitable for video‐frame‐rate imaging applications. 相似文献
27.
Sheikh M. Uddin Tanvir Mahmud Christoph Wolf Carsten Glanz Ivica Kolaric Christoph Volkmer Helmut Höller Ulrich Wienecke Siegmar Roth Hans-Jörg Fecht 《Composites Science and Technology》2010
Utilizing the extra-ordinary properties of carbon nanotube (CNT) in metal matrix composite (MMC) for macroscopic applications is still a big challenge for science and technology. Very few successful attempts have been made for commercial applications due to the difficulties incorporating CNTs in metals with up-scalable processes. CNT reinforced copper and copper alloy (bronze) composites have been fabricated by well-established hot-press sintering method of powder metallurgy. The parameters of CNT–metal powder mixing and hot-press sintering have been optimized and the matrix materials of the mixed powders and composites have been evaluated. However, the effect of shape and size of metal particles as well as selection of carbon nanotubes has significant influence on the mechanical and electrical properties of the composites. The hardness of copper matrix composite has improved up to 47% compared to that of pure copper, while the electrical conductivity of bronze composite has improved up to 20% compared to that of the pure alloy. Thus carbon nanotube can improve the mechanical properties of highly-conductive low-strength copper metals, whereas in low-conductivity high-strength copper alloys the electrical conductivity can be improved. 相似文献
28.
Mo Huang Dihu Chen Zhao Wang Jianping Guo Elias H. Dagher Bin Xu Ken Xu Hui Ye Weiguo Zheng Zhen Liang Xiaofeng Liang Wesley K. Masenten 《International Journal of Circuit Theory and Applications》2015,43(6):806-821
In this work, a power‐area‐efficient, 3‐band, 2‐RX MIMO, and TD‐LTE (backward compatible with the HSPA+, HSUPA, HSDPA, and TD‐SCDMA) CMOS receiver is presented and implemented in 0.13‐μm CMOS technology. The continuous‐time delta‐sigma A/D converters (CT ?Σ ADCs) are directly coupled to the outputs of the transimpedance amplifiers, eliminating the need of analog anti‐aliasing filters between RX front‐end and ADCs in conventional structures. The strong adjacent channel interference without low‐pass filter attenuation is handled by proper gain control. A low‐power small‐area solution for excess loop delay compensation is implemented in the CT ?Σ ADC. At 20 MHz bandwidth, the CT ?Σ ADC achieves 66 dB dynamic range and 3.5 dB RX chip noise figure is measured. A maximum of 2.4 dB signal‐to‐noise ratio degradation is measured in all the adjacent channel selectivity (ACS) and blocking tests, demonstrating the effectiveness of the strategy against the low‐pass filter removal from the conventional architecture. The receiver dissipates a maximum of 171 mW at 2‐RX MIMO mode. To our best knowledge, it is the first research paper on the design of fully integrated commercial TD‐LTE receiver. Copyright © 2014 John Wiley & Sons, Ltd. 相似文献
29.
30.
Claudio Bernardazzi Morgana Teixeira Lima Castelo-Branco Beatriz Pêgo Beatriz Elias Ribeiro Siane Lopes Bittencourt Rosas Patrícia Teixeira Santana Joo Carlos Machado Camille Leal Fabiano Thompson Robson Coutinho-Silva Heitor Siffert Pereira de Souza 《International journal of molecular sciences》2022,23(9)