Organized growth of GaAs/AlAs lateral structures on atomic step arrays: What is possible to do?

Laterally modulated nanostructures, exhibiting large optical and electrical anisotropy, can be grown an vicinal surfaces. However the lateral organization of Ga and Al atoms is far from ideal. We discuss our way of understanding the growth of these structures.     

Linear dichroism in a GaAs microcavity

Linear dichroism experiments show that exciton–polariton ground states are split into a linearly polarized doublet. At normal incidence and zero detuning this splitting does not exceed 10 μeV for the upper polariton branch and 3 μeV for the lower one. For both branches the splitting decreases with positive and negative detuning.     

Reduction of the hand representation in the ipsilateral primary motor cortex following unilateral section of the corticospinal tract at cervical level in monkeys

Background  

After sub-total hemi-section of cervical cord at level C7/C8 in monkeys, the ipsilesional hand exhibited a paralysis for a couple of weeks, followed by incomplete recovery of manual dexterity, reaching a plateau after 40–50 days. Recently, we demonstrated that the level of the plateau was related to the size of the lesion and that progressive plastic changes of the motor map in the contralesional motor cortex, particularly the hand representation, took place following a comparable time course. The goal of the present study was to assess, in three macaque monkeys, whether the hand representation in the ipsilesional primary motor cortex (M1) was also affected by the cervical hemi-section.     

Exciton-photon strong-coupling regime for a single quantum dot embedded in a microcavity

We report on the observation of the strong-coupling regime between the excitonic transition of a single GaAs quantum dot and a discrete optical mode of a microdisk microcavity. Photoluminescence is performed at various temperatures to tune the quantum dot exciton with respect to the optical mode. At resonance, we observe a clear anticrossing behavior, signature of the strong-coupling regime. The vacuum Rabi splitting amounts to 400 microeV and is twice as large as the individual linewidths.     

Measurement of the ratio of inclusive cross sections sigma(pp --> Z + b jet)/sigma(pp --> Z + jet) at square root(s) = 1.96 TeV

Using the data collected with the D0 detector at square root(s) = 1.96 TeV, for integrated luminosities of about 180 pb(-1), we have measured the ratio of inclusive cross sections for pp --> Z + b jet to pp --> Z + jet production. The inclusive Z + b-jet reaction is an important background to searches for the Higgs boson in associated ZH production at the Fermilab Tevatron collider. Our measurement is the first of its kind, and relies on the Z --> e+ e- and Z --> mu+ mu- modes. The combined measurement of the ratio yields 0.021+/-0.005 for hadronic jets with transverse momenta pT > 20 GeV/c and pseudorapidities absolute value(eta) < 2.5, consistent with next-to-leading-order predictions of the standard model.     

Measurement of the WW production cross section in pp collisions at square root[s]=1.96 TeV

We present a measurement of the W boson pair-production cross section in pp collisions at a center-of-mass energy of sqrt[s]=1.96 TeV. The data, collected with the Run II D0 detector at Fermilab, correspond to an integrated luminosity of 224-252 pb(-1) depending on the final state (ee, emu, or mumu). We observe 25 candidates with a background expectation of 8.1+/-0.6(stat)+/-0.6(syst)+/-0.5(lum) events. The probability for an upward fluctuation of the background to produce the observed signal is 2.3x10(-7), equivalent to 5.2 standard deviations. The measurement yields a cross section of 13.8(+4.3)(-3.8)(stat)+1.2-0.9(syst)+/-0.9(lum) pb, in agreement with predictions from the standard model.     

Specific heat experiments and critical concentration for ferromagnetism in nickel-platinum alloys

We have studied the electronic specific heat of various nickel-platinum alloys near the critical concentration for the appearance of ferromagnetism. The electronic specific heat coefficient has a maximum for an atomic concentration of 42.5 ± 0.5% nickel. This maximum coincides with that of the high field susceptibility. The results obtained are discussed qualitatively.     

Inclusive π0 production at the CERN p-p̄ collider

Inclusive π⁰ production has been measured at the CERN pp? collider, $\text{s}\text{=540}\text{GeV}$, for 90° production angle and in a range of transverse momenta between 1.5 and 4.5 GeV/c. The invariant production cross section is larger than that measured at $\text{s}\text{= 53}\text{GeV}$ for p-p collisions. The production of μ mesons aand of direct photons is also investigated.