A liquid-liquid extraction procedure followed by a low temperature purification step for the analysis of macrocyclic lactones in milk by liquid chromatography-tandem mass spectrometry and fluorescence detection

In this work a method is proposed and demonstrated for the analysis of the macrocyclic lactones abamectin, doramectin, eprinomectin, ivermectin and moxidectin in bovine milk by liquid chromatography coupled to mass spectrometry (LC-MS/MS) and liquid chromatography with fluorescence detection (LC-FL). The method is based on liquid-liquid extraction followed by a low temperature purification (LLE-LTP) step. Moreover, the proposed method was validated according to the Commission Decision 2002/657/EC, using LC-MS/MS and LC-FL for confirmatory and quantitative analysis, respectively. For LC-MS/MS the recovery rates observed ranged from 101.2 to 141.6% with coefficient of variation from 2.6 to 19.8%. For LC-FL the recovery rates observed ranged from 100.2 to 105% and coefficient of variations from 2.9 to 8.8%. Matrix effects were negligible due to the low temperature purification step. The quantification limits were far below the maximum limits established by regulations of all countries consulted. The proposed method proved to be simple, easy, and adequate for high-throughput analysis of a large number of samples per day at low cost.     

Supporting hydrogen based transportation: case studies with Global MARKAL Model

Steadily growing prices of oil and emissions coming from conventional vehicles, might force a switch to an alternative and less polluting fuel in the coming future. In this article we analyze the potential influence of selected factors for successful market penetration of hydrogen fuel cell vehicles in hydrogen based private transportation economy. Using a world scale, full energy system, bottom-up, optimization model (Global MARKAL Model—GMM) we address the possibility of supporting the fuel cell vehicle technology to become competitive in the markets. In a series of optimizations we evaluate the potential influence of governmental supports and the internalization of externalities related to CO₂ and local pollution emissions originating from the transportation sector, as well as preferential crediting options and demonstration projects promoting fuel cell vehicles. The results suggest that the crucial element is the price of fuel cells and their further potential to reduce costs. This reduction of costs may be triggered by governmental support such as direct subsidies to fuel cells, preferential crediting options for the buildup of hydrogen infrastructure as well as penalization of emitters of CO₂ and/or local pollutants.     

Experimental results from a tandem BWO-TWT system used to generatehigh-power microwaves

A relativistic backward wave oscillator (BWO) in tandem with a traveling wave tube (TWT) amplifier has been used to generate relatively long pulses of high-power X-band microwaves. In these experiments, a BWO is used to modulate the annular relativistic electron beam, which subsequently drives a TWT producing high-power microwave radiation. A special RF sever located between the two structures cuts off microwaves generated in the BWO from the TWT. Peak powers in excess of 100 MW are observed with overall beam-to-microwave efficiencies as high as 35%. By operating the BWO below saturation levels, pulse-shortening effects are minimized so that microwave pulses of duration comparable to that of the beam (100 ns) are possible. The operating frequency of the tandem system is tuned from 11 to 12 GHz by varying the effective energy of the beam     

Order parameter fluctuation spectrum and central peak in partially deuterated H-bonded ferroelectrics

The order parameter fluctuation spectrum in an isotopically disordered KH₂PO₄ type crystal has been evaluated as a function of the deuterium content using Mori's continued fraction representation. In contrast to a pure system we have now two narrow central peaks and two overdamped soft modes. The results show that the static central peak observed by light scattering in paraelectric KH₂PO₄ cannot be produced by naturally abundant deuterium.     

Efficient Computation of Roots in Finite Fields

We present an algorithm to compute rth roots in $\mathbb{F}_{q^m}We present an algorithm to compute rth roots in with complexity ?[(log m + r log q) m log q] if (m,q) = 1 and either (q(q−1),r) = 1 or r|(q−1) and ((q−1)/r,r) = 1. This compares well to previously known algorithms, which need O(r m³ log³ q) steps. Paulo S. L. M. Barreto: Supported by Scopus Tecnologia S. A. José Felipe Voloch: Supported by NSA grant MDA904-03-1-0117.     

Search for neutral, long-lived particles decaying into two muons in pp[over] collisions at sqrt[s]=1.96 TeV

We present a search for a neutral particle, pair produced in pp[over] collisions at sqrt[s]=1.96 TeV, which decays into two muons and lives long enough to travel at least 5 cm before decaying. The analysis uses approximately 380 pb(-1) of data recorded with the D0 detector. The background is estimated to be about one event. No candidates are observed, and limits are set on the pair-production cross section times branching fraction into dimuons + X for such particles. For a mass of 10 GeV and lifetime of 4x10(-11) s, we exclude values greater than 0.14 pb (95% C.L.). These results are used to limit the interpretation of NuTeV's excess of dimuon events.     

Search for ZH → l+ l- bb production in 4.2 fb(-1) of pp collisions at sqrt[s] =1 .96 TeV

We present a search for the standard model Higgs boson produced in association with a Z boson in 4.2 fb(-1) of pp collisions, collected with the D0 detector at the Fermilab Tevatron at sqrt[s] =1 .96 TeV. Selected events contain one reconstructed Z → e+ e- or Z → μ+ μ- candidate and at least two jets, including at least one b-tagged jet. In the absence of an excess over the background expected from other standard model processes, limits on the ZH cross section multiplied by the branching ratios are set. The limit at M(H) = 115 GeV is a factor of 5.9 larger than the standard model prediction.     

Search for long-lived particles decaying into electron or photon pairs with the D0 detector

In this Letter we report on a search for long-lived particles that decay into final states with two electrons or photons. Such long-lived particles arise in a variety of theoretical models, such as hidden valleys and supersymmetry with gauge-mediated breaking. By precisely reconstructing the direction of the electromagnetic shower we are able to probe much longer lifetimes than previously explored. We see no evidence of the existence of such long-lived particles and interpret this search as a quasi model-independent limit on their production cross section, as well as a limit on a long-lived fourth generation quark.     

Simultaneous measurement of the ratio R=B(t --> Wb)/B(t --> Wq) and the top-quark pair production cross section with the D0 detector at sqrt(s) = 1.96 TeV

We present the first simultaneous measurement of the ratio of branching fractions, R=B(t --> Wb)/B(t --> Wq), with q being a d, s, or b quark, and the top-quark pair production cross section sigma(tt[over]) in the lepton plus jets channel using 0.9 fb(-1) of pp[over] collision data at sqrt(s)=1.96 TeV collected with the D0 detector. We extract R and sigma(tt[over]) by analyzing samples of events with 0, 1, and > or =2 identified b jets. We measure R=0.97(+0.09)/(-0.08)(stat+syst) and sigma(tt[over])=8.18(+0.09)(-0.84)(stat+syst) +/- 0.50(lumi) pb, in agreement with the standard model prediction.     

Measurement of the forward-backward charge asymmetry in top-quark pair production

We present the first measurement of the integrated forward-backward charge asymmetry in top-quark-top-antiquark pair (tt) production in proton-antiproton (pp) collisions in the lepton+jets final state. Using a b-jet tagging algorithm and kinematic reconstruction assuming tt + X production and decay, a sample of 0.9 fb(-1) of data, collected by the D0 experiment at the Fermilab Tevatron Collider, is used to measure the asymmetry for different jet multiplicities. The result is also used to set upper limits on tt+X production via a Z' resonance.