408 research outputs found
A Study of the Intermetallic Compound Growth in Flip-Chip Packages under Thermal Loading
The intermetallic compound layers in solder bumps have the brittle feature and can easily fracture under thermal or mechanical loading. Therefore, the intermetallic compound is an issue for the fracture reliability of the solder bumps. In this work, the intermetallic compound growth before and after high temperature storage tests was investigated. The experiment results revealed that the solder bumps with nickel layers could reduce the intermetallic compound growth rate. The nickel layer, which was added in between Cu and SnAg for top solder bumps, was an important factor controlling the intermetallic compound thickness. It was hard to tell the intermetallic compound thickness at time zero; at the time of 147 hours, the intermetallic compound grew to 3.25 µm; at the time of 294 hours, the intermetallic compound grew to 5.25 µm. However, the solder joints were still in good condition
Recent results from parton cascade and microscopic transport
Parton cascade is a microscopic transport approach for the study of the
space-time evolution of the Quark-Gluon Plasma produced in relativistic heavy
ion collisions and its experimental manifestations. In the following, parton
cascade calculations on elliptic flow and thermalization will be discussed.
Dynamical evolution is shown to be important for the production of elliptic
flow including the scaling and the breaking of the scaling of elliptic flow.
The degree of thermalization is estimated using both an elastic parton cascade
and a radiative transport model. A longitudinal to transverse pressure ratio,
, is shown to be expected in the central cell in central
collisions. This provides information on viscous corrections to the ideal
hydrodynamical approach.Comment: Presented at Hot Quarks 2008, Estes Park, Colorado, USA, 18-23 August
200
Quarkonia Measurements with STAR
We report results on quarkonium production from the STAR experiment at the
Relativistic Heavy-Ion Collider (RHIC). J/psi spectra in p+p and Cu+Cu
collisions at sqrt(s) = 200 GeV with transverse momenta in the range of 0.5-14
GeV/c and 5-8 GeV/c, respectively, are presented. We find that for p_T > 5
GeV/c yields in p+p collisions are consistent with those in minimum-bias Cu+Cu
collisions scaled with the respective number of binary nucleon-nucleon
collisions. In this range the nuclear modification factor, R_AA, is measured to
be 0.9+-0.2(stat). For the first time at RHIC, high-p_T J/psi-hadron
correlations were studied in p+p collisions. Implications from our measurements
on J/psi production mechanisms, constraints on open bottom yields, and J/psi
dissociation mechanisms at high-p_T are discussed. In addition, we give a brief
status of measurements of Upsilon production in p+p and Au+Au collisions and
present projections of future quarkonia measurements based on an upgrades to
the STAR detector and increased luminosity achieved through stochastic cooling
of RHIC.Comment: 5 pages, 5 figures. Prepared for 3rd International Conference on Hard
and Electromagnetic Probes of High-Energy Nuclear Collisions (Hard Probes
2008), A Toxa, Spain, June 8-14, 200
Nernst effect of iron pnictide and cuprate superconductors: signatures of spin density wave and stripe order
The Nernst effect has recently proven a sensitive probe for detecting unusual
normal state properties of unconventional superconductors. In particular, it
may sensitively detect Fermi surface reconstructions which are connected to a
charge or spin density wave (SDW) ordered state, and even fluctuating forms of
such a state. Here we summarize recent results for the Nernst effect of the
iron pnictide superconductor , whose ground state evolves
upon doping from an itinerant SDW to a superconducting state, and the cuprate
superconductor which exhibits static stripe
order as a ground state competing with the superconductivity. In , the SDW order leads to a huge Nernst response, which allows
to detect even fluctuating SDW precursors at superconducting doping levels
where long range SDW order is suppressed. This is in contrast to the impact of
stripe order on the normal state Nernst effect in . Here, though signatures of the stripe order are
detectable in the temperature dependence of the Nernst coefficient, its overall
temperature dependence is very similar to that of ,
where stripe order is absent. The anomalies which are induced by the stripe
order are very subtle and the enhancement of the Nernst response due to static
stripe order in as compared to that of the
pseudogap phase in , if any, is very small.Comment: To appear in: 'Properties and applications of thermoelectric
materials - II', V. Zlatic and A. Hewson, editors, Proceedings of NATO
Advanced Research Workshop, Hvar, Croatia, September 19 -25, 2011, NATO
Science for Peace and Security Series B: Physics and Biophysics, (Springer
Science+Business Media B.V. 2012
Probing Ion-Ion and Electron-Ion Correlations in Liquid Metals within the Quantum Hypernetted Chain Approximation
We use the Quantum Hypernetted Chain Approximation (QHNC) to calculate the
ion-ion and electron-ion correlations for liquid metallic Li, Be, Na, Mg, Al,
K, Ca, and Ga. We discuss trends in electron-ion structure factors and radial
distribution functions, and also calculate the free-atom and metallic-atom
form-factors, focusing on how bonding effects affect the interpretation of
X-ray scattering experiments, especially experimental measurements of the
ion-ion structure factor in the liquid metallic phase.Comment: RevTeX, 19 pages, 7 figure
J/psi production in relativistic heavy ion collisions from a multi-phase transport model
Using A Multi-Phase Transport (AMPT) model, we study J/psi production from
interactions between charm and anti-charm quarks in initial parton phase and
between D and Dbar mesons in final hadron phase of relativistic heavy ion
collisions at the Relativistic Heavy Ion Collider (RHIC). Including also the
inverse reactions of J/psi absorption by gluons and light mesons, we find that
the net number of J/psi from the parton and hadron phases is smaller than that
expected from the superposition of initial nucleon-nucleon collisions, contrary
to the J/psi enhancement predicted by the kinetic formation model. The
production of J/psi is further suppressed if one includes the color screening
effect in the parton phase. We have also studied the dependence of J/psi
production on the charm quark mass and the effective charm meson mass.Comment: Figures redone with better statistic
Ultrastrong conductive in situ composite composed of nanodiamond incoherently embedded in disordered multilayer graphene
Traditional ceramics or metals cannot simultaneously achieve ultrahigh strength and high electrical conductivity. The elemental carbon can form a variety of allotropes with entirely different physical properties, providing versatility for tuning mechanical and electrical properties in a wide range. Here, by precisely controlling the extent of transformation of amorphous carbon into diamond within a narrow temperature–pressure range, we synthesize an in situ composite consisting of ultrafine nanodiamond homogeneously dispersed in disordered multilayer graphene with incoherent interfaces, which demonstrates a Knoop hardness of up to ~53 GPa, a compressive strength of up to ~54 GPa and an electrical conductivity of 670–1,240 S m(–1) at room temperature. With atomically resolving interface structures and molecular dynamics simulations, we reveal that amorphous carbon transforms into diamond through a nucleation process via a local rearrangement of carbon atoms and diffusion-driven growth, different from the transformation of graphite into diamond. The complex bonding between the diamond-like and graphite-like components greatly improves the mechanical properties of the composite. This superhard, ultrastrong, conductive elemental carbon composite has comprehensive properties that are superior to those of the known conductive ceramics and C/C composites. The intermediate hybridization state at the interfaces also provides insights into the amorphous-to-crystalline phase transition of carbon
Plane-wave impulse approximation extraction of the neutron magnetic form factor from quasielastic 3He(e,e′) at Q2=0.3 to 0.6 (GeV/c)2
A high precision measurement of the transverse spin-dependent asymmetry AT′ in 3He(e,e′) quasielastic scattering was performed in Hall A at Jefferson Lab at values of the squared four-momentum transfer, Q2, between 0.1 and 0.6 (GeV/c)2. AT′ is sensitive to the neutron magnetic form factor, GMn. Values of GMn at Q2=0.1 and 0.2 (GeV/c)2, extracted using Faddeev calculations, were reported previously. Here, we report the extraction of GMn for the remaining Q2 values in the range from 0.3 to 0.6 (GeV/c)2 using a plane-wave impulse approximation calculation. The results are in good agreement with recent precision data from experiments using a deuterium target
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