Time-bin-modulated biphotons from cavity-enhanced down-conversion

We have generated a new type of biphoton state by cavity-enhanced down-conversion in a type-II phase-matched, periodically poled KTiOPO4 crystal. By introducing a weak intracavity birefringence, we obtained signal and idler photons whose quantum interference was modulated between singlet and triplet signatures according to their arrival-time difference. This cavity-enhanced biphoton source is spectrally bright, yielding a single-mode fiber-coupled coincidence rate of 0.7 pairs/s per mW of pump power per MHz of down-conversion bandwidth.     

Optimization of laser-focused deposition lines: Rydberg atoms

Optimally narrow nanoscale lines are computationally obtained for Rb Rydberg atoms deposited on surfaces. The use of optimized polychromatic fields is shown to allow lines as narrow as 1 nm in the absence of transverse velocities and shown to counter the deleterious effects of transverse velocities in laser cooled beams. Specifically, lines as narrow as 6.5 nm wide are obtained in the presence of transverse velocities associated with a temperature of 1 mK. Using this approach it is possible to deposit a single narrow line, even when the atomic beam is bigger than the period of the focusing lens, using as few as two, relatively weak, laser fields.     

Lattice dynamics and structural phase transitions

Results of lattice dynamics, or atomic motions in a solid, explain many of the thermodynamic properties of solids. Inelastic neutron scattering conveniently explores the atomic motions, quantized as phonons. Of particular interest are materials that undergo structural phase transitions. The soft mode theory has been successful in relating anomalous phonon behavior to structural changes in solids. One such example is the ferromagnetic shape memory alloy, Ni₂MnGa, which undergoes a sequence of phase transitions leading to a magnetic, incommensurate modulated, tetragonal phase as the ground state. The experiments, coupled with first principles calculations, provide evidence that strong electron–phonon coupling is the driving mechanism of the phase transformation.     

Microcirculatory fraction (MCF(I)) as a potential imaging marker for tumor heterogeneity in breast cancer

Cancer is a heterogeneous disease by nature. Current imaging studies usually ignore intratumor variability in imaging biomarkers. We postulate that quantifying tumor heterogeneity with imaging techniques can provide useful information about cancer biology and potentially serve as novel imaging biomarkers. In this retrospective study, we identify a potential imaging marker, the microcirculatory fraction (MCF(I)), that quantifies tumor heterogeneity in normoxic/hypoxic cellular composition. We demonstrate its application on a test population of 22 women with stage II/III HER-2 negative breast cancer receiving antiangiogenic-cytotoxic combination neoadjuvant chemotherapy. Early change in MCF(I) (ΔMCF(I)) is assessed with dynamic contrast enhanced magnetic resonance imaging at the end of Cycle 2 and associated with pathologic response. Its performance is compared with other established volumetric imaging biomarkers (initial tumor volume and volume change) by statistical and graphic methods. We demonstrate that a significant (P<.01) difference in ΔMCF(I) can be detected between good (median ΔMCF(I) 0.27) and poor (median ΔMCF(I) -0.12) responders, despite the limited population size. Differences in the volumetric biomarkers are not statistically significant. Receiver operating characteristic analysis also shows that ΔMCF(I) is a good predictor for pathologic response (AUC=0.86, 95% CI 0.69-1.00, P<.01), while predictions made with the established volumetric biomarkers are not significantly better than random guesses. We conclude that ΔMCF(I) has the potential of being a better predictive biomarker for therapeutic response assessment. Our findings support our postulation that quantifying tumor heterogeneity with imaging techniques can provide additional information that can serve as novel biomarkers.     

The superconductive states in the dislocation structures

On the basis of an analysis of the Ginzburg-Landau equations it is shown that in the dislocation structures above the critical temperature and the critical magnetic field of homogeneous superconductor there is an unhomogeneous superconductive order parameter. Such states may be either localized for the single dislocation and the dislocations pile-up or delocalized for periodical systems. The temperature shift, the critical field and the current are investigated.     

Evidence for anchimeric assistance in the expulsion of bromine from ring-substituted β-phenylethyl bromides: When is a simple cleavage a rearrangement?

Using the principles of the quasi-equilibrium theory, substituent effects, deuterium labeling and comparison of compound behavior, we provide strong evidence for aryl participation in the expalsion of Br· from the molecular ion of β-phenylethyl bromide and eleven of its ringsubstitued derivatives. This reaction shows a kinetic behavior which is typical of rearrangements, its activation energy is lower than that of similar reactions where participation is partially or completely precluded and substitute effects are not only consistent with a particular process, but are also consistent with those predicted from solution chemistry.     

Competition cusps in (α, γ) reactions

Absolute cross sections are presented for the reactions ³⁷Cl(α, γ)⁴¹K for 2.90 MeV ≦ E^lab_α ≦ 5.23 MeV, ${}^{62}\text{Ni}\text{(α, γ)}{}^{66}\text{Zn}\text{for}\text{5.07}\text{MeV}\text{≦ E}{}_{\mathrm{\alpha }}{}^{\mathrm{?2}}\text{lab}\text{≦ 8.64}\text{MeV}\text{,}{}^{62}\text{Ni}\text{(α,}\text{n}\text{)}{}^{65}\text{Zn}$ for energies near the (α, n₀) threshold at $\text{E}{}_{\mathrm{\alpha }}{}^{\mathrm{<mtext>lab</mtext>}}\text{= 6.90}\text{MeV up to}\text{8.76}\text{MeV}\text{,}{}^{64}\text{Ni}\text{(α, γ)}{}^{68}\text{Zn for}\text{4.50 ≦ E}{}_{\mathrm{\alpha }}{}^{\mathrm{<mtext>lab</mtext>}}\text{≦ 7.45}\text{MeV}$, and for ⁶⁴Ni(α, n)⁶⁷N from E_α^lab = 5.30 MeV up to E_α = 7.45 MeV. Substantial competition cusps were observed in the excitation function for all three (α, γ) reactions. The data were found to be in reasonable agreement with the predictions of the current versions of global Hauser-Feshbach models used in nucleosynthesis calculations. Including width fluctuation corrections and realistic neutron strength functions generally improves the ability of the models to predict the depth of the (α, γ) competition cusps; the depths of the predicted (α,γ) cusps are insensitive to the degree of isospin mixing. Taken together with studies of competition effects in proton-induced reactions, the present data confirm the importance of width fluctuation and strength function effects, and indicate essentially complete isospin mixing between T^< and T^> states in the compound nucleus.