7,582 research outputs found
Cosmic Chemical Evolution
Numerical simulations of standard cosmological scenarios have now reached the
degree of sophistication required to provide tentative answers to the
fundamental question: Where and when were the heavy elements formed? Averaging
globally, these simulations give a metallicity that increases from 1% of the
solar value at to 20% at present. This conclusion is, in fact,
misleading, as it masks the very strong dependency of metallicity on local
density. At every epoch higher density regions have much higher metallicity
than lower density regions. Moreover, the highest density regions quickly
approach near solar metallicity and then saturate, while more typical regions
slowly catch up. These results are much more consistent with observational data
than the simpler picture (adopted by many) of gradual, quasi-uniform increase
of metallicity with time.Comment: ApJ(Letters) in press, 15 latex pages and 4 figure
The Linear Model under Mixed Gaussian Inputs: Designing the Transfer Matrix
Suppose a linear model y = Hx + n, where inputs x, n are independent Gaussian
mixtures. The problem is to design the transfer matrix H so as to minimize the
mean square error (MSE) when estimating x from y. This problem has important
applications, but faces at least three hurdles. Firstly, even for a fixed H,
the minimum MSE (MMSE) has no analytical form. Secondly, the MMSE is generally
not convex in H. Thirdly, derivatives of the MMSE w.r.t. H are hard to obtain.
This paper casts the problem as a stochastic program and invokes gradient
methods. The study is motivated by two applications in signal processing. One
concerns the choice of error-reducing precoders; the other deals with selection
of pilot matrices for channel estimation. In either setting, our numerical
results indicate improved estimation accuracy - markedly better than those
obtained by optimal design based on standard linear estimators. Some
implications of the non-convexities of the MMSE are noteworthy, yet, to our
knowledge, not well known. For example, there are cases in which more pilot
power is detrimental for channel estimation. This paper explains why
Adiabatic Gate Teleportation
The difficulty in producing precisely timed and controlled quantum gates is a
significant source of error in many physical implementations of quantum
computers. Here we introduce a simple universal primitive, adiabatic gate
teleportation, which is robust to timing errors and many control errors and
maintains a constant energy gap throughout the computation above a degenerate
ground state space. Notably this construction allows for geometric robustness
based upon the control of two independent qubit interactions. Further, our
piecewise adiabatic evolution easily relates to the quantum circuit model,
enabling the use of standard methods from fault-tolerance theory for
establishing thresholds.Comment: 4 pages, 1 figure, with additional 3 pages and 2 figures in an
appendix. v2 Refs added. Video abstract available at
http://www.quantiki.org/video_abstracts/0905090
Matching model of flow table for networked big data
Networking for big data has to be intelligent because it will adjust data
transmission requirements adaptively during data splitting and merging.
Software-defined networking (SDN) provides a workable and practical paradigm
for designing more efficient and flexible networks. Matching strategy in the
flow table of SDN switches is most crucial. In this paper, we use a
classification approach to analyze the structure of packets based on the
tuple-space lookup mechanism, and propose a matching model of the flow table in
SDN switches by classifying packets based on a set of fields, which is called
an F-OpenFlow. The experiment results show that the proposed F-OpenFlow
effectively improves the utilization rate and matching efficiency of the flow
table in SDN switches for networked big data.Comment: 14 pages, 6 figures, 2 table
Recovering a Classically Oral Homiletic
Historically, the preaching of the word of God has been a synthesis of both oral and written orientations with text providing both the source and the preservation of the sermon, and orality fueling its expression. Expression preceded documentation. Scripture displays this dual nature in its revelation, expression and transmission. But with the technologizing of the word in typographic literacy, sermons became increasingly conditioned by the literate sensorium and lost many of their oral psychodynamics. Character, wisdom, dialogue, memory, responsiveness, and flexibility were exchanged for private preparation, literate structuring, and literary delivery. Sermons became disembodied, existing more reliably in externalized text.
Walter Ong provides the framework for the reappraisal of communicative history by strategically forgetting the pervasive influence of technology. Recovering the older resources of orality, Ong restores a sense of balance to the oral/literate continuum by returning to the primarily oral orientations of the Greco-Roman world of classic rhetoric, and rehabilitates rhetoric with theological and homiletic implications.
Quintilian\u27s infinitely flexible oratory represents the richness of the communicative environment during the infancy of the church. His emphasis on depth of understanding as a prerequisite for public speaking grounds the speaker in resources beyond the pragmatics of the specific situation or topic, and can be profitably applied to contemporary homiletic praxis. Quintilian\u27s understanding of oral composition, memory, roadmapping, and kairos is applicable to the kind of preparation and delivery required by an intentional move toward an orally-conditioned homiletic
âMulti-directional managementâ: Exploring the challenges of performance in the World Class Programme environment
Driven by the ever-increasing intensity of Olympic competition and the âno compromise â no stone unturnedâ requirements frequently addressed by HM Government and its main agency, UK Sport, a change in culture across Olympic team landscapes is a common occurrence. With a focus on process, this paper presents reflections from eight current or recently serving UK Olympic sport Performance Directors on their experiences of creating and disseminating their vision for their sport, a vital initial activity of the change initiative. To facilitate a broad overview of this construct, reflections are structured around the visionâs characteristics and foundations, how it is delivered to key stakeholder groups, how it is influenced by these groups, the qualities required to ensure its longevity and its limitations. Emerging from these perceptions, the creation and maintenance of a shared team vision was portrayed as a highly dynamic task requiring the active management of a number of key internal and external stakeholders. Furthermore, the application of âdarkâ traits and context-specific expertise were considered critical attributes for the activityâs success. Finally, recent calls for research to elucidate the wider culture optimisation process are reinforced
Multi-Use Facilities - Repurposing Facilities Infrastructure to Support the Multi-customer Environment
Since the early 90âs the space launch business has undergone significant change in customers, composition, capacity, and key players. These changes have a resultant effect upon the spaceport industry. Some spaceports, in their current state, may not survive the probable future market and business environment. To stay in the game, spaceports are reexamining their target launch vehicles, services, and operations philosophy. One of the strategies being developed to accommodate current and future changes is to repurpose facilities to support multiple customers. The new vision is that multiple commercial, as well as government entities, having multiple spacecraft and launch vehicle configurations will all operate within or upon one multi-purpose facility â including launch pads. One of the challenges is to develop capability for the âfirst to marketâ vehicles without increasing price or risk to future users. This presentation will provide the considerations involved in developing facility infrastructure to support the multi-customer environment
Market Impact in Trader-Agents:Adding Multi-Level Order-Flow Imbalance-Sensitivity to Automated Trading Systems
Financial markets populated by human traders often exhibit "market impact",
where the traders' quote-prices move in the direction of anticipated change,
before any transaction has taken place, as an immediate reaction to the arrival
of a large (i.e., "block") buy or sell order in the market: e.g., traders in
the market know that a block buy order will push the price up, and so they
immediately adjust their quote-prices upwards. Most major financial markets now
involve many "robot traders", autonomous adaptive software agents, rather than
humans. This paper explores how to give such trader-agents a reliable
anticipatory sensitivity to block orders, such that markets populated entirely
by robot traders also show market-impact effects. In a 2019 publication Church
& Cliff presented initial results from a simple deterministic robot trader,
ISHV, which exhibits this market impact effect via monitoring a metric of
imbalance between supply and demand in the market. The novel contributions of
our paper are: (a) we critique the methods used by Church & Cliff, revealing
them to be weak, and argue that a more robust measure of imbalance is required;
(b) we argue for the use of multi-level order-flow imbalance (MLOFI: Xu et al.,
2019) as a better basis for imbalance-sensitive robot trader-agents; and (c) we
demonstrate the use of the more robust MLOFI measure in extending ISHV, and
also the well-known AA and ZIP trading-agent algorithms (which have both been
previously shown to consistently outperform human traders). We demonstrate that
the new imbalance-sensitive trader-agents introduced here do exhibit market
impact effects, and hence are better-suited to operating in markets where
impact is a factor of concern or interest, but do not suffer the weaknesses of
the methods used by Church & Cliff. The source-code for our work reported here
is freely available on GitHub.Comment: To be presented at the 13th International Conference on Agents and
Artificial Intelligence (ICAART2021), Vienna, 4th--6th February 2021. 15
pages; 9 figure
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