On the passive limited slip differential for high performance vehicle applications

The paper is aimed at a comprehensive revision of the working principles and limitations of the mechanical limited slip differential, the traditional, passive device used to improve traction capabilities and to extend the performance envelope of high performance road cars, racing and rally cars. Its impact on vehicle handling through a yaw moment generated with passive torque distribution across the drive axle is investigated by means of vehicle dynamics simulations

Rubik: fast analytical power management for latency-critical systems

Latency-critical workloads (e.g., web search), common in datacenters, require stable tail (e.g., 95th percentile) latencies of a few milliseconds. Servers running these workloads are kept lightly loaded to meet these stringent latency targets. This low utilization wastes billions of dollars in energy and equipment annually. Applying dynamic power management to latency-critical workloads is challenging. The fundamental issue is coping with their inherent short-term variability: requests arrive at unpredictable times and have variable lengths. Without knowledge of the future, prior techniques either adapt slowly and conservatively or rely on application-specific heuristics to maintain tail latency. We propose Rubik, a fine-grain DVFS scheme for latency-critical workloads. Rubik copes with variability through a novel, general, and efficient statistical performance model. This model allows Rubik to adjust frequencies at sub-millisecond granularity to save power while meeting the target tail latency. Rubik saves up to 66% of core power, widely outperforms prior techniques, and requires no application-specific tuning. Beyond saving core power, Rubik robustly adapts to sudden changes in load and system performance. We use this capability to design RubikColoc, a colocation scheme that uses Rubik to allow batch and latency-critical work to share hardware resources more aggressively than prior techniques. RubikColoc reduces datacenter power by up to 31% while using 41% fewer servers than a datacenter that segregates latency-critical and batch work, and achieves 100% core utilization.National Science Foundation (U.S.) (Grant CCF-1318384

AISLAMIENTO Y PURIFICACIÓN DEL HONGO ECTOMICORRÍZICO Helvella lacunosa EN DIFERENTES MEDIOS DE CULTIVO

Helvella lacunosa, besides its mycorrhizal importance for plant forest species, has a high commercial value. The commercial production of H. lacunosa represents two main advantages: Economical benefits for the communities able to produce it; and conservation of biodiversity in the forests by preventing the species overexploitation and maintaining the mushroom-plants micorrhizal relationship. Carrying out this perspective requires, in principle, to isolate the species mycelium, and then to develop the mycorrhizing technique that allows the production of the mushroom. Isolating the mycelium by the first time, however, involves testing several culture media in order to identify the potential requirements for inducing the myceliums growth. In the present work we tested, in laboratory, five different agar-based culture media to isolate H. lacunosas mycelium, and to evaluate its growing rate, analysis of covariance showed that there is a simple linear relationship between incubation time and the diameter. Indicating that the cumulative growth rate of the mycelium, was different between the culture media (F4, 240 = 17,008, p <0.001). The APD medi u m had the highest growth rate followed by AEA. In both growing media, the diameter of the mycelium converges the fifth day. The lowest growth rate was presented in the media AEM and AEP

Analysis of interval‐grouped data in weed science: The binnednp Rcpp package

[Abstract] Weed scientists are usually interested in the study of the distribution and density functions of the random variable that relates weed emergence with environmental indices like the hydrothermal time (HTT). However, in many situations, experimental data are presented in a grouped way and, therefore, the standard nonparametric kernel estimators cannot be computed. Kernel estimators for the density and distribution functions for interval‐grouped data, as well as bootstrap confidence bands for these functions, have been proposed and implemented in the binnednp package. Analysis with different treatments can also be performed using a bootstrap approach and a Cramér‐von Mises type distance. Several bandwidth selection procedures were also implemented. This package also allows to estimate different emergence indices that measure the shape of the data distribution. The values of these indices are useful for the selection of the soil depth at which HTT should be measured which, in turn, would maximize the predictive power of the proposed methods. This paper presents the functions of the package and provides an example using an emergence data set of Avena sterilis (wild oat). The binnednp package provides investigators with a unique set of tools allowing the weed science research community to analyze interval‐grouped data.Ministerio de Economía y Competitividad; AGL2015-64130-RMinisterio de Economía y Competitividad; MTM2014-52876-RMinisterio de Economía y Competitividad; MTM2017-82724-RMinisterio de Economía y Competitividad; AGL2012-33736Xunta de Galicia; ED431C-2016-015Xunta de Galicia; ED431G/0

A Cautionary Tale: MARVELS Brown Dwarf Candidate Reveals Itself To Be A Very Long Period, Highly Eccentric Spectroscopic Stellar Binary

We report the discovery of a highly eccentric, double-lined spectroscopic binary star system (TYC 3010-1494-1), comprising two solar-type stars that we had initially identified as a single star with a brown dwarf companion. At the moderate resolving power of the MARVELS spectrograph and the spectrographs used for subsequent radial-velocity (RV) measurements (R ~ <30,000), this particular stellar binary mimics a single-lined binary with an RV signal that would be induced by a brown dwarf companion (Msin(i)~50 M_Jup) to a solar-type primary. At least three properties of this system allow it to masquerade as a single star with a very low-mass companion: its large eccentricity (e~0.8), its relatively long period (P~238 days), and the approximately perpendicular orientation of the semi-major axis with respect to the line of sight (omega~189 degrees). As a result of these properties, for ~95% of the orbit the two sets of stellar spectral lines are completely blended, and the RV measurements based on centroiding on the apparently single-lined spectrum is very well fit by an orbit solution indicative of a brown dwarf companion on a more circular orbit (e~0.3). Only during the ~5% of the orbit near periastron passage does the true, double-lined nature and large RV amplitude of ~15 km/s reveal itself. The discovery of this binary system is an important lesson for RV surveys searching for substellar companions; at a given resolution and observing cadence, a survey will be susceptible to these kinds of astrophysical false positives for a range of orbital parameters. Finally, for surveys like MARVELS that lack the resolution for a useful line bisector analysis, it is imperative to monitor the peak of the cross-correlation function for suspicious changes in width or shape, so that such false positives can be flagged during the candidate vetting process.Comment: 16 pages, 11 figures, 6 table

Very Low Mass Stellar and Substellar Companions to Solar-Like Stars From MARVELS V: A Low Eccentricity Brown Dwarf from the Driest Part of the Desert, MARVELS-6b

We describe the discovery of a likely brown dwarf (BD) companion with a minimum mass of 31.7 +/- 2.0 M_Jup to GSC 03546-01452 from the MARVELS radial velocity survey, which we designate as MARVELS-6b. For reasonable priors, our analysis gives a probability of 72% that MARVELS-6b has a mass below the hydrogen-burning limit of 0.072 M_Sun, and thus it is a high-confidence BD companion. It has a moderately long orbital period of 47.8929 +0.0063/-0.0062 days with a low eccentricty of 0.1442 +0.0078/-0.0073, and a semi-amplitude of 1644 +12/-13 m/s. Moderate resolution spectroscopy of the host star has determined the following parameters: T_eff = 5598 +/- 63, log g = 4.44 +/- 0.17, and [Fe/H] = +0.40 +/- 0.09. Based upon these measurements, GSC 03546-01452 has a probable mass and radius of M_star = 1.11 +/- 0.11 M_Sun and R_star = 1.06 +/- 0.23 R_Sun with an age consistent with less than ~6 Gyr at a distance of 219 +/- 21 pc from the Sun. Although MARVELS-6b is not observed to transit, we cannot definitively rule out a transiting configuration based on our observations. There is a visual companion detected with Lucky Imaging at 7.7 arcsec from the host star, but our analysis shows that it is not bound to this system. The minimum mass of MARVELS-6b exists at the minimum of the mass functions for both stars and planets, making this a rare object even compared to other BDs.Comment: 15 pages, 15 figures, 5 tables. Accepted for publication in The Astronomical Journa

Chemical abundance analysis of three α-poor, metal-poor stars in the ultrafaint dwarf galaxy Horologium I

We present chemical abundance measurements of three stars in the ultrafaint dwarf galaxy Horologium I, a Milky Way satellite discovered by the Dark Energy Survey. Using high-resolution spectroscopic observations, we measure the metallicity of the three stars, as well as abundance ratios of several α-elements, iron-peak elements, and neutron-capture elements. The abundance pattern is relatively consistent among all three stars, which have a low average metallicity of [Fe/H]∼−2.6 and are not α-enhanced ([α/Fe]∼0.0). This result is unexpected when compared to other low-metallicity stars in the Galactic halo and other ultrafaint dwarfs and suggests the possibility of a different mechanism for the enrichment of Hor I compared to other satellites. We discuss possible scenarios that could lead to this observed nucleosynthetic signature, including extended star formation, enrichment by a Population III supernova, and or an association with the Large Magellanic Cloud

Single and multi-antenna MC-DS-CDMA with joint detection for broadband block-fading channels

In the context of broadband wireless communications using code division multiple access (CDMA), the main multiple access (MA) options include single-carrier direct sequence CDMA (SC-DS-CDMA) using time-domain direct sequence spreading [1, p. 728], multicarrier CDMA (MC-CDMA) using frequency-domain spreading [2, 3] and multicarrier DS-CDMA (MC-DS-CDMA) using time-domain direct sequence spreading of the individual sub-carrier signals [4, 5]. It was shown in [6] that MC-DS-CDMA has the highest degrees of freedom in the family of CDMA schemes that can be beneficially exploited during the system design and reconfiguration procedures. An amalgam of MC-CDMA and MC-DS-CDMA known as time and frequency domain spreading (TF-domain spreading) MC-DS-CDMA was proposed in [6]. TF-domain spreading MC-DS-CDMA has several benefits over conventional MC-DS-CDMA with regard to both capacity and performance [7]. However, in contrast to conventional MC-DS-CDMA, TF-domain spreading MC-DS-CDMA introduces MUI, which necessitates the use of joint detection at the receiver. Recently, multiple input multiple output (MIMO) or multi-antenna TF-domain spreading MC-DS-CDMA schemes have been proposed in the literature that e ciently exploit both the spatial and frequency diversity available in MIMO frequency-selective channels [8, 9]. Although an extensive amount of research has been done on single and multi-antenna TF-domain spreading MC-DS-CDMA schemes that achieve both spatial and frequency diversity in frequency-selective slow fading channels [6–9], very little research considers the time-selectivity of the wireless channels encountered. Thus, the above-mentioned schemes may not be su ciently e cient, when communicating over wireless channels exhibiting both frequency-selective and time-selective fading. There are very few MC-DS-CDMA schemes in the literature that consider the time-selectivity of the wireless channels encountered. This study considers the design of single and multi-antenna TF-domain spreading MC-DS-CDMA, for frequency-selective block-fading channels, which are capable of exploiting the full diversity available in the channel (i.e. spatial, frequency and temporal diversity), using various methods of joint detection at the receiver. It has been shown that the diversity gain in block-fading channels can be improved by coding across multiple fading blocks [10–12]. Single-antenna TF-domain spreading MC-DS-CDMA is considered for the quasi-synchronous uplink channel, and multi-antenna TF-domain spreading MC-DS-CDMA is considered for the synchronous downlink channel. Numerous simulated bit error rate (BER) performance curves, obtained using a triply selective MIMO channel platform, are presented in this study using optimal and sub-optimal joint detection algorithms at the receiver. In addition, this study investigates the impact of spatial correlation on the BER performance of the MC-DS-CDMA schemes considered. From these simulated results, one is able to conclude that TF-domain spreading MC-DS-CDMA designed for frequency-selective block-fading channels performs better than previously proposed schemes designed for frequency-selective slow fading channels, owing to the additional temporal diversity exploited under the block-fading assumption. AFRIKAANS : In die konteks van bre¨eband- draadlose kommunikasie deur die gebruik van kodeverdelingveelvuldige toegang (KVVT) behels die belangrikste veelvuldigetoegang- (VT) opsies enkel-draer direkte-sekwensie KVVT (ED-DS-KVVT), deur die gebruik van tyd-domein direkte sekwensie-verspreiding [1, p. 728], veelvuldigedraer-KVVT (VD-KVVT) deur die gebruik van frekwensiedomein-verspreiding [2, 3] en VD-DS- KVVT deur die gebruik van tyd-domein direkte sekwensie-verspreiding van die individuele sub-draerseine [4, 5]. Daar is in [6] aangetoon dat VD-DS-KVVT die hoogste vlakke van vryheid in die familie KVVT-skemas het wat voordelig benut kan word gedurende sisteemontwerp en rekonfigurasieprosedures. ’n Amalgaam van VD-KVVT en VD-DS-KVVT bekend as tyd-en-frekwensiedomeinverspreiding (TF-domeinverspreiding) VD-DS-KVVT is voorgestel in [6]. TF-domeinverspreiding VD-DS-KVVT het verskeie voordele bo konvensionele VD-DS-KVVT wat sowel kapasiteit as werkverrigting betref [7]. In teenstelling met konvensionele VD-DS-KVVT benut TF-domeinverspreiding VD-DS-KVVT multi-gebruiker-interferensie, wat die gebruik van gesamentlike opsporing by die ontvanger noodsaak. In die onlangse verlede is in die literatuur veelvuldige-inset-veelvuldige-uitset- (VIVU) of veelvuldige-antenna TF-omeinverspreiding VD-DS-KVVT-skemas voorgestel wat sowel die ruimtelike as frekwensiediversiteit wat in VIVU frekwensie-selektiewe kanale beskikbaar is, e ektief gebruik [8, 9]. Hoewel uitgebreide navorsing onderneem is oor enkel- en multi-antenna TF-domeinverspreiding VD-DS-KVVT-skemas wat sowel ruimtelike as frekwensie diversiteit in frekwensie-selektiewe stadig deinende kanale bereik [6–9], oorweeg baie min navorsing die tyd-selektiwiteit van die draadlose kanale wat betrokke is. Bogenoemde skemas mag dus nie e ektief genoeg wees nie wanneer kommunikasie plaasvind oor draadlose kanale wat sowel frekwensie-selektiewe as tyd-selektiewe wegsterwing toon. Baie min VD-DS-KVVT-skemas in die literatuur skenk aandag aan die tyd-selektiwiteit van die betrokke draadlose kanale. Die studie ondersoek die ontwerp van enkel- en multi-antenna TF-domeinverspreiding VD-DS-KVVT vir frekwensie-selektiewe blokwegsterwingkanale, wat in staat is om die volle diversiteit wat in die kanaal beskikbaar is, te benut (i.e. ruimtelike, frekwensie- en tyddiversiteit), deur die gebruik van verskeie metodes van gesamentlike opsporing by die ontvanger. Daar is aangetoon dat die diversiteitwins in blokwegsterwingkanale verbeter kan word deur kodering oor veelvuldige deinende blokke [10–12]. Enkel-antenna TF-domeinverspreiding VD-DS-KVVT word oorweeg vir die kwasi-sinchroniese opverbinding-kanaal, en multi-antenna TF-domeinverspreiding VD-DS-KVVT vir die sinchroniese afverbinding-kanaal. Talryke gesimuleerde bisfouttempo (BFT) werkverrigtingkurwes wat verkry is deur die gebruik van ’n drie-voudige selektiewe VIVU-kanaalplatform, word in hierdie studie aangebied, deur die gebruik van optimale en sub-optimale gesamentlike opsporingsalgoritmes by die ontvanger. Daarbenewens ondersoek hierdie studie die impak van ruimtelike korrelasie op die BFT-werkverrigring van die VD-DS-KVVT-skemas wat oorweeg word. Uit hierdie gesimuleerde resultate is dit moontlik om tot die gevolgtrekking te kom dat TF-domeinverspreiding VD-DS-KVVT wat ontwerp is vir frekwensie-selektiese blokwegsterwingkanale beter werkverrigting toon as vroe¨er voorgestelde skemas wat ontwerp is vir frekwensie-selektiewe stadig deinende kanale, te danke aan die ekstra tyddiversiteit wat deur die blokwegsterwing-aanname benut word. CopyrightDissertation (MEng)--University of Pretoria, 2010.Electrical, Electronic and Computer Engineeringunrestricte