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Search Results: 1 - 10 of 216363 matches for " Qiu L "
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Evaluation of In-Use Fuel Economy for Hybrid and Regular Transit Buses  [PDF]
Shauna L. Hallmark, Bo Wang, Yu Qiu, Robert Sperry
Journal of Transportation Technologies (JTTs) , 2013, DOI: 10.4236/jtts.2013.31006

Fuel costs are a significant portion of transit agency budgets. Hybrid technology offers an attractive option and has the potential to significantly reduce operating costs for agencies. The main impetus behind use of hybrid transit vehicles is fuel savings and reduced emissions. Laboratory tests have indicated that hybrid transit buses can have significantly higher fuel economy and lower emissions compared to conventional transit buses. However, the number of studies is limited and laboratory tests may not represent actual driving conditions since in-use vehicle operation differs from laboratory test cycles. Several initial studies have suggested that the fuel economy savings reported in laboratory tests may not be realized on-road. The objective of the project described in this paper was to evaluate the in-use fuel economy differences between hybrid-electric and conventional transit buses for the Ames, Iowa (USA) transit authority. On-road fuel economy was evaluated over a 12-month period for 12 hybrid and 7 control transit buses. Fuel economy comparisons were also provided for several older in-use bus types. Buses other than the control and hybrid buses were grouped by model year corresponding to US diesel emission standards. Average fuel economy in miles per gallon was calculated for each bus group overall and by season. Hybrid buses had the highest fuel economy for all time periods for all bus types. Hybrid buses had a fuel economy that was 11.8% higher than control buses overall and was 12.2% higher than buses with model years 2007 and higher, 23.4% higher than model years 2004 to 2006, 10.2% higher than model years 1998 to 2003, 38.1% higher than for model years 1994 to 1997, 36.8% higher for model years 1991 to 1993, and 36.8% higher for model years pre-1991. Differences between groups of buses also varied by season of the year.

Crash Modification Factors for Dynamic Speed Feedback Signs on Rural Curves  [PDF]
Shauna L. Hallmark, Yu Qiu, Neal Hawkins, Omar Smadi
Journal of Transportation Technologies (JTTs) , 2015, DOI: 10.4236/jtts.2015.51002
Abstract: A large number of crashes occur on curves even though they account for only a small percentage of a system’s mileage. Excessive speed has been identified as a primary factor in both lane departure and curve-related crashes. A number of countermeasures have been proposed to reduce driver speeds on curves, which ideally result in successful curve negotiation and fewer crashes. Dynamic speed feedback sign (DSFS) systems are traffic control devices that have been used to reduce vehicle speeds successfully and, subsequently, crashes in applications such as traffic calming on urban roads. DSFS systems show promise, but they have not been fully evaluated for rural curves. To better understand the effectiveness of DSFS systems in reducing crashes on curves, a national field evaluation of DSFS systems on curves on rural two lane roadways was conducted. Two different DSFS systems were selected and placed at 22 sites in seven states. Control sites were also identified. A full Bayes modeling methodology was utilized to develop crash modification factors (CMFs) for several scenarios including total crashes for both directions, total crashes in the direction of the sign, total single-vehicle crashes, and single-vehicle crashes in the direction of the sign. Using quarterly crash frequency as the response variable, crash modification factors were developed and results showed that crashes were 5% to 7% lower after installation of the signs depending on the model.
Melt Infiltration Casting Of Zr57Al10Nb5Cu15.4Ni12.6 Amorphous Matrix Composite  [PDF]
K.Q. Qiu, Y.L. Ren
Journal of Minerals and Materials Characterization and Engineering (JMMCE) , 2004, DOI: 10.4236/jmmce.2004.32010
Abstract: The Zr57Al10Nb5Cu15.4Ni12.6 bulk metallic glass-forming alloy is reinforced with tungsten fiber. Cylindrical samples up to 6.3 mm in diameter and 7cm in length have been synthesized using melt infiltration casting method. The structure and microstructure of the composites processed in typical conditions were analyzed by x-ray diffraction and scanning electron microscopy. The suitable interface reaction and fully amorphous matrix can only be obtained through the combination of a suitable infiltration temperature and time. The processing conditions were more rigorous compared to those of making Zr-Ti-Ni-Cu-Be matrix composite due to intermetallic compound nucleation when exposed to the tungsten fibers. A technique map, including infiltrating temperature and time is presented in this paper.
Differential Cross Section for Higgs Boson Production Including All-Orders Soft Gluon Resummation
Edmond L. Berger,Jianwei Qiu
Physics , 2002, DOI: 10.1103/PhysRevD.67.034026
Abstract: The transverse momentum $Q_T$ distribution is computed for inclusive Higgs boson production at the energy of the CERN Large Hadron Collider. We focus on the dominant gluon-gluon subprocess in perturbative quantum chromodynamics and incorporate contributions from the quark-gluon and quark-antiquark channels. Using an impact-parameter $b$-space formalism, we include all-orders resummation of large logarithms associated with emission of soft gluons. Our resummed results merge smoothly at large $Q_T$ with the fixed-order expectations in perturbative quantum chromodynamics, as they should, with no need for a matching procedure. They show a high degree of stability with respect to variation of parameters associated with the non-perturbative input at low $Q_T$. We provide distributions $d\sigma/dy dQ_T$ for Higgs boson masses from $M_Z$ to 200 GeV. The average transverse momentum at zero rapidity $y$ grows approximately linearly with mass of the Higgs boson over the range $M_Z < m_h <200$ GeV, $ \simeq 0.18 m_h + 18 $~GeV. We provide analogous results for $Z$ boson production, for which we compute $ \simeq 25$ GeV. The harder transverse momentum distribution for the Higgs boson arises because there is more soft gluon radiation in Higgs boson production than in $Z$ production.
Study on the Theoretical Limitation of the Mid-Infrared PbSe N+-P Junction Detectors at High Operating Temperature  [PDF]
Xinghua Shi, Quang Phan, Binbin Weng, Lance L. McDowell, Jijun Qiu, Zhihua Cai, Zhisheng Shi
Detection (Detection) , 2018, DOI: 10.4236/detection.2018.61001
Abstract: This paper provides a theoretical study and calculation of the specific detectivity-D* limit of photovoltaic (PV) mid-wave infrared (MWIR) PbSe n+-p junction detectors operating at both room temperature and TE-cooled temperature. For a typical PbSe p-type doping concentration of 2 × 1017 cm-3 and with high quantum efficiency, the D* limits of a photovoltaic PbSe n+-p junction detector are shown to be 2.8 × 1010 HZ1/2/W and 3.7 × 1010 HZ1/2/W at 300 K and 240 K, with cut-off wavelength of 4.5 μm and 5.0 μm, respectively. It is almost one magnitude higher than the current practical MWIR PV detector. Above 244 K, the detector is Johnson noise limited, and below 191 K the detector reaches background limited infrared photodetector (BLIP) D*. With optimization of carrier concentration, D* and BLIP temperature could be further increased.
A Novel OFDM Channel Estimation Algorithm with ICI Mitigation over Fast Fading Channels
C. Tao,J. Qiu,L. Liu
Radioengineering , 2010,
Abstract: Orthogonal frequency-division multiplexing (OFDM) is well-known as a high-bit-rate transmission technique, but the Doppler frequency offset due to the high speed movement destroys the orthogonality of the subcarriers resulting in the intercarrier interference (ICI), and degrades the performance of the system at the same time. In this paper a novel OFDM channel estimation algorithm with ICI mitigation based on the ICI self-cancellation scheme is proposed. With this method, a more accurate channel estimation is obtained by comb-type double pilots and then ICI coefficients can be obtained to mitigate the ICI on each subcarrier under the assumption that the channel impulse response (CIR) varies in a linear fashion. The theoretical analysis and simulation results show that the bit error rate (BER) and spectral efficiency performances are improved significantly under high-speed mobility conditions (350 km/h – 500 km/h) in comparison to ZHAO’s ICI self-cancellation scheme.
Isolated Prompt Photon Cross Sections
Edmond L. Berger,Xiaofeng Guo,Jianwei Qiu
Physics , 1996,
Abstract: We show that the conventionally defined partonic cross section for the production of isolated prompt photons is not an infrared safe quantity. We work out the case of $e^+e^-\to\gamma + X$, and discuss implications for hadron reactions.
Breakdown of Conventional Factorization for Isolated Photon Cross Sections
Edmond L. Berger,Xiaofeng Guo,Jianwei Qiu
Physics , 1995, DOI: 10.1103/PhysRevLett.76.2234
Abstract: Using $e^+e^-\rightarrow\gamma + X$ as an example, we show that the conventional factorization theorem in perturbative quantum chromodynamics breaks down for isolated photon cross sections in a well defined part of phase space. Implications and physical consequences are discussed.
Inclusive Prompt Photon Production in Hadronic Final States of $e^+e^-$ Annihilation
Edmond L. Berger,Xiaofeng Guo,Jianwei Qiu
Physics , 1995, DOI: 10.1103/PhysRevD.53.1124
Abstract: We provide complete analytic expressions for the inclusive prompt photon production cross section in hadronic final states of $e^+e^-$ annihilation reactions through one-loop order in quantum chromodynamics perturbation theory. Computed explicitly are direct photon production through first order in the electromagnetic strength $\alpha_{em}$ and the quark-to-photon and gluon-to-photon fragmentation contributions through first order in the strong coupling $\alpha_s$. The full angular dependence of the cross sections is displayed, separated into transverse $(1 +\cos ^2\theta _\gamma)$ and longitudinal $(\sin ^2\theta_\gamma)$ components, where $\theta_\gamma$ specifies the direction of the photon with respect to the $e^+e^-$ collision axis. We discuss extraction of fragmentation functions from $e^+e^-$ data.
Isolated Prompt Photon Production in Hadronic Final States of $e^+e^-$ Annihilation
Edmond L. Berger,Xiaofeng Guo,Jianwei Qiu
Physics , 1996, DOI: 10.1103/PhysRevD.54.5470
Abstract: We provide complete analytic expressions for the isolated prompt photon production cross section in $e^+e^-$ annihilation reactions through one-loop order in quantum chromodynamics (QCD) perturbation theory. Functional dependences on the isolation cone size $\delta$ and isolation energy parameter $\epsilon$ are derived. The energy dependence as well as the full angular dependence of the cross section on $\theta_\gamma$ are displayed, where $\theta_\gamma$ specifies the direction of the photon with respect to the $e^+e^-$ collision axis. We point out that conventional perturbative QCD factorization breaks down for isolated photon production in $e^+e^-$ annihilation reactions in a specific region of phase space. We discuss the implications of this breakdown for the extraction of fragmentation functions from $e^+e^-$ annihilation data and for computations of prompt photon production in hadron-hadron reactions.
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