Discrete and generalized phase space techniques in critical quantum spin chains

We apply the Wigner function formalism from quantum optics via two approaches, Wootters' discrete Wigner function and the generalized Wigner function, to detect quantum phase transitions in critical spin-$\frac{1}{2}$ systems. We develop a general formula relating the phase space techniques and the thermodynamical quantities of spin models, which we apply to single, bipartite and multi-partite systems governed by the XY and the XXZ models. Our approach allows us to introduce a novel way to represent, detect, and distinguish first-, second- and infinite-order quantum phase transitions. Furthermore, we show that the factorization phenomenon of the XY model is only directly detectable by quantities based on the square root of the bipartite reduced density matrix. We establish that phase space techniques provide a simple, experimentally promising tool in the study of many-body systems and we discuss their relation with measures of quantum correlations and quantum coherence.     

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X-ray photoelectron spectroscopy (XPS) has become popular for polymeric and biological surface analysis. However, several experimental factors may bias XPS data interpretation. Ex situ contamination, outgassing, reactions due to ultra-high vacuum or X-ray exposure, and charging problems are not uncommon. They are reflected in the high variability of data quality of recent reports. In order to enhance the reliability and reproducibility of XPS data, especially for organics and polymers, a suitable in situ reference material would be of a great help. At Aalto's CHEM XPS laboratory, we use 100% cellulosic filter paper as a reference for all XPS experiments. Nature derived macrofibrillar cellulose is not an obvious candidate for an in situ reference material in XPS; however, it is not only the most abundant biopolymer on the biosphere but it also qualifies surprisingly well as a generic in situ XPS reference.     

Synthesis,characterization, and photopolymerization of (meth)acrylate-functional polyisobutylene macromers produced by cleavage/alkylation of butyl rubber

Linear, multi-functional polyisobutylene (PIB) macromers bearing pendent and terminal (meth)acrylate moieties were prepared via electrophilic cleavage/alkylation of butyl rubber in the presence of (3-bromopropoxy)benzene, followed by displacement of the resulting bromide moieties with potassium (meth)acrylate. Number average functionality (F_n) ranged from 2.8–7.9; functional equivalent weights ranged from 2.3–4.7 kg/mol. For comparison, a three-arm, end-functional PIB triacrylate with equivalent weight of 3.3 kg/mol was also synthesized via living polymerization and end quenching with 4-phenoxy-1-butyl acrylate. All polymers were photocured using Darocur 1173 photoinitiator, and curing kinetics were monitored by real time Fourier-transform infrared spectroscopy. All systems reached ~100% conversion by 1,800 s, but the linear macromers displayed slower curing rates compared to the PIB triacrylate. The curing rate of linear macromers increased as molecular weight decreased. Cured networks were characterized using dynamic mechanical analysis and tensile testing. Tensile strength varied from 0.15–0.80 MPa. Young's modulus varied from 0.13–1.8 MPa. Strain at break for most networks ranged from 34–54%, but the network derived from the lowest molecular weight PIB reached 113% at failure. Percent extractables, measured using solvent extraction, was about 2% for linear macromers and about 4% for PIB triacrylate.     

Laser beam widening mechanisms in turbid media

We examine theoretically and experimentally the transverse intensity profile of a laser beam as it traverses through a turbid medium. By increasing the concentrations of milk in an aqueous solution we examine the transition from the weakly scattering to the diffusive regime. The experimental data of the transverse beam profiles for various scattering strengths are obtained in a non-contact geometry from digital images of the exit surface of the medium. The intensity distributions are compared with theoretical data obtained from Monte Carlo simulations.     

Continuous dependence on modeling for nonlinear ill-posed problems

The nonlinear ill-posed Cauchy problem , where A is a positive self-adjoint operator on a Hilbert space H, χ∈H, and h:[0,T)×H→H is a uniformly Lipschitz function, is studied in order to establish continuous dependence results for solutions to approximate well-posed problems. The authors show here that solutions of the problem, if they exist, depend continuously on solutions to corresponding approximate well-posed problems, if certain stabilizing conditions are imposed. The approximate problem is given by , v(0)=χ, for suitable functions f. The main result is that , where C and M are computable constants independent of β and 0<β<1. This work extends to the nonlinear case earlier results by the authors and by Ames and Hughes.     

Probing shell structure and shape changes in neutron-rich sulfur isotopes through transient-field g-factor measurements on fast radioactive beams of 38S and 40S

The shell structure underlying shape changes in neutron-rich nuclei near N = 28 has been investigated by a novel application of the transient-field technique to measure the first-excited-state g factors in 38S and 40S produced as fast radioactive beams. There is a fine balance between proton and neutron contributions to the magnetic moments in both nuclei. The g factor of deformed 40S does not resemble that of a conventional collective nucleus because spin contributions are more important than usual.     

Measurement of high-pT single electrons from heavy-flavor decays in p + p collisions at square root of s = 200 GeV

The momentum distribution of electrons from decays of heavy flavor (charm and bottom) for midrapidity absolute value of y < 0.35 in p + p collisions at square root of s = 200 GeV has been measured by the PHENIX experiment at the BNL Relativistic Heavy Ion Collider over the transverse momentum range 0.3 < pT < 9 GeV/c. Two independent methods have been used to determine the heavy-flavor yields, and the results are in good agreement with each other. A fixed-order-plus-next-to-leading-log perturbative QCD calculation agrees with the data within the theoretical and experimental uncertainties, with the data/theory ratio of 1.71+/-0.02stat+/-0.18sys for 0.3 < pT < 9 GeV/c. The total charm production cross section at this energy has also been deduced to be sigma cc = 567+/-57stat+/-193sys microb.     

Measurement of excited states in (40)Si and evidence for weakening of the N=28 shell gap

Excited states in (40)Si have been established by detecting gamma rays coincident with inelastic scattering and nucleon removal reactions on a liquid hydrogen target. The low excitation energy, 986(5) keV, of the 2(1)(+) state provides evidence of a weakening in the N=28 shell closure in a neutron-rich nucleus devoid of deformation-driving proton collectivity.     

Partitioning a Planar Graph of Girth 10 into a Forest and a Matching

We prove that any finite planar graph with girth at least 10 can have its edges partitioned to form two graphs on the same vertices, one of which is a forest, and the other of which is a matching. Several related results are also demonstrated.     

Functional Reduction and Mental Causation

Over the past few decades, Jaegwon Kim has argued that non-reductive physicalism is an inherently unstable position. In his view, the most serious problem is that non-reductive physicalism leads to type epiphenomenalism—the causal inefficacy of mental properties. Kim suggests that we can salvage mental causation by endorsing functional reduction. Given the fact that Kim’s goal in formulating functional reduction is to provide a robust account of mental causation it would be surprising if his position implies eliminativism about mental properties or leads to a view that is similar to one of the versions of non-reductive physicalism that he criticizes. We will show that depending on how certain key claims are interpreted, there are reasons for thinking functional reduction has these implications, in which case either Kim fails to provide a robust account of mental causation or there is reason to suspect that some of his criticisms of non-reductive physicalism are misguided.