Parton distributions for high energy collisions

Recent data from deep inelastic scattering experiments atx10^–2 are used to fix the parton distributions down tox10^–4 andQ ²0.3 GeV². The predicted extrapolations are uniquely determined by the requirement of avalence-like structure ofall parton distributions at some low resolution scale and are furthermore shown to be insensitive in the small-x region, 10^–4x10^–2, to the detailed experimental input at the presently accessiblex>10^–2. Simple parameterizations of the resulting parton distributions are presented in the range 10^–5x<1 and=">Q ²10⁸ GeV² as obtained from the leading- and higher-order evolution equations.     

Cytoplasmic Changes in Cardiac Cells During a Contraction Cycle Detected by Fluorescence Polarization

Intracellular structural changes, occurring in a cardiac myocyte during a contraction cycle, were investigated by means of intracellular fluorescein fluorescence polarization (IFFP), in comparison to cytoplasmic concentration of Ca²⁺ [Ca²⁺]_i measured by indo-1. A simple physical model is presented. It assumes a biphase intracellular matrix, differing in its potency to restrict hosting fluorescent probe mobility. The first is a mobile nonrestricting phase, made mostly of aqua (aqua zone), while the second is a mobile-restricting phase, allocated mainly at the proximity of the filament sites. Their physicochemical properties such as [Ca²⁺], viscosity, and pH, may differ, thereby influencing the hosting probe fluorescence characteristics differently. These possible influences were examined experimentally. Based on experimental data, the model enables the evaluation, to first order of approximation, of the relative number of fluorescent probes populating the two phases and the time variation viscosity (_r(t)) of the mobile-restricting filament zones taking place throughout the contraction cycle.     

Magnetic properties of Fe and Ni films evaporated in poor vacuum

To examine the pressure dependence of magnetic characteristics of Fe and Ni films, the films were prepared in vacuum ranging from 10^–5 to 10^–2 torr.Saturation magnetizationM _s ^* , perpendicular anisotropyK ^* and coercive forceH _c for Fe and Ni films deposited at around 10^–5 torr were in good agreement with the values obtained by others. When the film thickness was less than 500 ,M _s ^* for Fe films increased with pressure, while it decreased monotonically for Ni films. At pressures between 2×10^–3 and 10^–2 torr,M _s ^* decreased rapidly for Fe but it increased slightly for Ni. This interesting behaviour was most marked with film thickness of about 500 . Corresponding to the change inM _s ^* , bothK ^* andH _c also changed with deposition pressure.The result should be explained in terms of the presence of Fe₄N, Fe₈N and Ni₃N, as well as the macroscopic and microscopic structures of films.     

Improved slow-positron yield using a single crystal tungsten moderator

A well-annealed W(110) single crystal was used as a fast-to-slow positron moderator. The measured moderator efficiency at room temperature using a⁵⁸Co positron source in the backscattering geometry is =(3.2±0.4)×10^–3, roughly a factor of three better than for the best previously reported Cu(111)+S moderator. We find a stable positron moderation efficiency over a period of several weeks when maintained at pressures around 10^–9 Torr and an energy spreadE = 0.7 eV of the emitted slow positrons. An initial attempt was made to fabricate a hybrid Cu on W(110) moderator, which yielded of about 1.2×10^–3 after annealing.     

Galaxy formation just after the recombination period

A scenario of galaxy formation is outlined which is based essentially on the fact that the cosmic matter about 10⁶yr after the end of the recombination period is a general relativistic Boltzmann gas very close to equilibrium. In this scenario the observed very small inhomogeneities of the background radiation lead to very sharply edged gas clouds in the centres of the inhomogeneities. The universe between the clouds is completely swept clean of matter. If one assumes the centres of the inhomogeneities to be axially symmetric, the mass spectrum of the clouds extends from the smallest globular clusters withM 10⁵ M as the lower limit (spherical symmetry) up to the big spiral galaxies withM 10¹¹ M as the upper limit (maximal flattening). The upper limit masses are extremely thin pancakes which contract within a time interval of about 2 · 10⁹ years to the proportions of an ordinary spiral galaxy of today.     

Lepton flavour violating heavy Higgs decays within the and their detection at the LHC

Within the νMSSM, a Minimal Supersymmetric neutrino See-saw Model, Lepton Flavour Violating Higgs couplings are strongly enhanced at large tanβ (30), which can lead to BR(H⁰/A⁰→τμ)O(10⁻⁴), for M_H⁰/A⁰160 GeV. Enhancements on the production of Higgs bosons, through the gluon fusion mechanism, gg→H⁰/A⁰, and the associated production channel , whose rates grow with tanβ, as well as the mass degeneracy that occurs between the H⁰ and A⁰ states in this regime, also contribute to further the possibilities to detect a heavy Higgs signal into τμ pairs. We show that the separation of τμ Higgs events from the background at the upcoming CERN Large Hadron Collider could be done for Higgs masses up to about 600 GeV for 300 fb⁻¹ of luminosity, for large tanβ values. However, even with as little as 10 fb⁻¹ one can probe H⁰/A⁰ masses up to 400 GeV or so, if tanβ=60. Altogether, these processes then provide a new Higgs discovery mode as well as an independent test of flavour physics.     

Ion mixing in Al,Si, and their oxides

The redistribution of thin metallic markers due to ion irradiation was studied by backscattering spectrometry in Al, Al₂O₃, Si, and SiO₂. Marker species were selected for their similar masses and different chemical reactivities with the host media and included Ti, Fe, W, Pt, and Au. It was found that the marker signals are Gaussian and that the variance ² of the marker atom distributions increases linearly with the dose of the irradiation, is insensitive to the temperature of irradiation in the range of 80–300 K, and depends linearly on the nuclear stopping power of the incident ions. The absolute values of ² for Ti, Fe, W, Pt, and Au markers in Al and Al₂O₃, W, and Pt in SiO₂ and W in Si is, within±50 %, of 6.5×10³Å² for 300 keV, 8×10¹⁵ Xe ions/cm². These observations suggest that collisional cascade mixing is a dominant mechanism in this type of impurity-matrix combinations. Only Au and Pt in Si mix at a larger rate: ² for Pt is about 3 and for Au about 5 times larger than ² for all other markers. Lower threshold displacement energies and/or the contribution of processes other than cascade mixing are possible considered reasons. In polycrystalline Al, a rapid migration of Au and Pt atoms throughout the Al layer, similar to grain boundary diffusion, is observed.     

Two distinguishable fluorescent modes of 1-anilino-8-naphthalenesulfonate bound to human albumin

We study the interaction of 1-anilino-8-naphthalenesulfonate (ANS) with human (HSA) and bovine serum albumin (BSA) by phase and modulation fluorescence spectroscopy. We determined that both HSA and BSA show one or two distinguishable fluorescent sites, depending of the ANS/serum albumin ratio. At above a 11 ANS/HSA molar ratio, the steady-state emission spectra for ANS can be resolved in two components: component 1, emitting with a lifetime (₁) of 16 ns and a _1max of 478 nm, with a quantum yield (_f1) of 0.67, and component 2, with a lifetime (₂) of 2–4 ns and a _2max of 483 nm, with an average quantum yield (_f2) of about 0.11. Considering these findings, the binding analysis is fitted with a model of two independent sites. Site 1 has an association constantK _as1=0.87×10⁶M^–1 and a capacity of 1.04 mol of ANS/mol of HSA, and site 2 aK _as2=0.079×10⁶M^–1 and a capacity of 2.34 mol of ANS/mol of HSA. Analysis of fluorescence lifetime distributions shows that the rigidity of the fluorophore environment at site 1 changes when site 2 is occupied. These findings suggest an interconnection between the two sites and that ligands can stabilize the protein's globular structure. To assess the identity of the ANS binding sites we used diazepam as a marker of the site located at the IIIA HSA subdomain and aspirin as a marker of sites located at the IIIA and IIA HSA subdomains. Both ligands displace ANS only from site 1, suggesting that it corresponds to the binding site located at the IIIA sub-domain of the protein. We determined that theK _as values for diazepam and aspirin are 0.113× 10⁶ and 0.021×10⁶ M ^–1 respectively.     

Muonium in ultra-pure and Si-doped germanium

The influence of the isoelectronic impurity silicon ([Si]=10¹²–10¹⁸ cm^–3) on the spin precession signals of positive muons in ultra-pure germanium crystals is investigated between 5 and 340 K in transverse magnetic fields of 0.5 to 27.5 mT. Normal (isotropic) muonium atoms Mu are formed in all samples with about the same probability ( 0.7). Down to quite low temperatures (20 K) Mu is found to diffuse very rapidly through the Ge matrix and to become ionized by interaction with the Si atoms. Another ionization process, presumably due to the screening of the ⁺ by the increasing number of free charge carriers, sets in at about 180 K.     

Space- and time-resolved investigation of gain lines in Na-like copper

We report space- and time-resolved measurements of the gain coefficient for four gain lines in sodium-like copper. The lines investigated include the twon = 1 transitions 5g–4f and 5f–4d at 11.1 nm and 10.3nm and the twon = 2 transitions 6g–4f and 6f–4d at 7.2 nm, and 6.9 nm. The investigations were carried out for four irradiation intensities from 4 × 10¹² W/cm² to 3 × 10¹³ W/cm² using the Asterix IV high-power iodine laser at Garching (wavelength 1.315 µm, pulse duration 450 ps).The main results may be summarized as follows: On varying the laser intensity it was found that the highest values of the gain could be seen at an irradiation of 8 × 10¹² W/cm². For then = 1 lines the spatial maximum of the gain occurred at a distance of 300 µm from the target, and for then = 2 lines at 200 µm. The temporal gain maximum occurred at a time of 1.8 ns after the pulse maximum. The gain values range up to 2.6 cm^–1.Dedicated to the memory of the late Prof. Shi-shen Chen, who contributed to the early phase of this work     

Semi-insulating electrical properties of undoped inp after heat treatment in a phosphorus atmosphere

Nominally undoped InP wafers have been annealed in a phosphorus atmosphere under a pressure of about 5 bar at temperatures of 900 °C for about 80 h. It was found that the electrical properties of the samples changed considerably after this treatment. A room temperature resistivity of up to 2×10⁷cm (semi-insulating behaviour) was obtained in the bulk of the samples. The resistivity finally obtained depends on the starting carrier concentration of the untreated samples. The Hall coefficient and Hall mobility have been measured up to 600 °C. The results can be interpreted in terms of a deep electronic level (E _A=0.63 ... 0.65 eV below the conduction band). The Hall coefficient was always found to be negative resulting in a Hall mobility of 1.4 to 4.9×10³ cm²/Vs. The highest resistivity in nominally undoped bulk InP so far reported in the literature [1] was =3.6 × 10⁵cm. Therefore, this paper demonstrates for the first time that a really semi-insulating behaviour of >10⁷ cm can be achieved for bulk InP with the purity of nominally undoped material (10¹⁵ to 10¹⁶cm^–3).     

The electric field gradient at iodine impurities in zinc and cadmium

The electric quadrupole interaction at iodine implanted in zinc and cadmium single crystals is investigated, using the - perturbed angular correlation technique. The results show that the implanted¹²⁹Te and¹³²Te isotopes occupy two well-defined sites, identified by the electric field gradient parameters. One fraction of the impurities is substitutionally implanted, witheq _zz=–1.49(9)10¹⁸ and –1.58(15)10¹⁸V/cm², in Zn and Cd respectively. The other fraction is identified as an impurity-divacancy configuration with |eq _zz |=3.81(8)10¹⁸V/cm²; =0.72(4) for Zn and |eq _zz |=3.55(11)10¹⁸V/cm²; =0.53(13) for Cd. The electronic enhancement in the electric fieldgradient at the substitutional site equalsK=–0.66 and –0.56 respectively and follows the empirical trend ofK versus the impurity valence for the s-p elements in Zinc.     

Search for the Dirac monopole by means of vavilov-cherenkov radiation at the 70 Gev IHEP (Institute for High Energy Physics Serpukhov) proton synchrotron

At the proton energy of 70 GeV on the internal target of the IHEP proton synchrotron the search was made for magnetic charges over the Vavilov-Cherenkov radiation and characteristic polarization. Eight Cherenkov counters of a special construction served as detectors. Possible events were recorded with two fast five-ray oscillographs triggered by 6-fold coincidences. The efficiency of the magnetic charge recording was about 10%.The proton beam of 6.4×10¹⁴ intensity traversed the target-radiator; and not a single case of the production of the Dirac monopole with the magnetic charge from minimal one of about 2/3g _D (g _D =68.5e) up to2g _D was recorded. This means that in the conditions of our experiment the upper boundary of the cross section of the Dirac monopole production by 70 GeV protons per nucleon of Si and O nuclei for magnetic charges of masses from 3 up to 5·5m_p was found to be(95%) 10^–40 cm².On leave fromDepartment of Nuclear Physics, Comenius University, Bratislava, Czechoslovakia.The authors express their gratitude to the workers of the enterprise Dioptra (Turnov, SSR) for making of optical details for the device for SDM.     

Theoretical analysis of trapping and recombination of photogenerated carriers in amorphous silicon solar cells

We have made theoretical studies on the trapping and recombination of photogenerated carriers in hydrogenated amorphous silicon (a-SiH) p-i-n solar cells. We discuss in detail the following points: 1) The limitations of the assumptions in the previous analysis. It has been clarified that the single-level Shockley-Read-Hall model for carrier recombination and the treatment of trap occupation in terms of quasi-Fermi levels are inadequate for exact analysis. 2) The superlinear dependence of carrier recombination rate on the free-carrier density which can explain the enhancement of photo-induced changes ina-SiH under high intensity light. 3) The estimation of capture cross section of the tail states ina-SiH. We show that the charged and neutral tail states have rather small capture cross sections of less than 10^–16 cm² and of less than 10^–19 cm², respectively. 4) The effect of the recombination of photogenerated (PG) carriers at the p/i and the n/i interfaces. We estimate the recombination velocityS of PG carriers at these interfaces to be about 10³ cm/s. It has been also clarified that the decrease inS is effective to improve the cell performance, especially the open circuit voltage.     

Investigation of the isospin-forbidden reaction6Li(6Li,d 2)10 B 0+,1

Angular distributions of the isospin-forbidden reaction⁶Li(⁶Li, d₂)¹⁰ B _0+,1 were measured at six beam energies in the range from 3 to 8 MeV. The contribution of two-step transfer mechanism to the reaction under consideration was found to be negligible. Hauser-Feshbach model cross sections, obtained with parameters derived from a previous analysis of isospin-allowed reactions in the⁶Li +⁶Li system are consistent with the data, provided a 2% reduction factor reflecting isospin mixing of compound nucleus levels. From this factor an isospin-breaking matrix element of H _c ^{2 1/2}13 keV was deduced. The presence of one broad or several resonances with (J ^P ,T)=(1^–, 1) or (2^–,1) concentrated at an excitation energy of about 30.3 MeV in¹²C seems to be responsible for the observed shape of angular distributions and their energy dependence.This work was supported by Deutsche Forschungsgesellschaft under contact No. Fr575/2-1,2.     

Neutron damage and annealing studies of copper-doped silicon solar cells

The effects of Cu-doping, oxygen and dopant on the fast neutron radiation damage of silicon solar cells are studied in this paper. The diffusion length damage coefficientK _L is defined as K_L= (1/L _i ² – 1/L _o ² )^–1= (1/L²)^–1. The (1/L²) values of n/p-type cells, measured at 300 and 80K, are smaller by about one order in magnitude than those of p/n-type cells. Characteristic curves of (1/L ²) values versus total neutron flux of p/n, n/p and copper-doped n/p-type cells begin to deviate from a 45° straight line around a total neutron flux of 10¹² to 10¹³ n cm^–2. The effect of copper-doping on the radiation resistant property is observed with high resistivity bulk n/p-type (20 to 40 -cm) cells, but not with low resistivity bulk n/p-type (10 -cm) cells at 300K. Values of (1/L ²) versus neutron flux, measured at 80K, are not affected by copper-doping, bulk dopant and oxygen concentration in the bulk region of n/p-type cells. The isochronal annealing of silicon solar cells depends on the total neutron flux, copper-doping and carrier injection during the annealing process. Namely, copper-doping and carrier injection enhance the annealing process of the neutron-induced defect clusters in n/p-type cells.     

A limit theorem for stochastic acceleration

We consider the motion of a particle in a weak mean zero random force fieldF, which depends on the position,x(t), and the velocity,v(t)= (t). The equation of motion is (t)=F(x(t),v(t), ), wherex(·) andv(·) take values in ^d ,d3, and ranges over some probability space. We show, under suitable mixing and moment conditions onF, that as 0,v (t)v(t/²) converges weakly to a diffusion Markov processv(t), and ² x (t) converges weakly to , wherex=lim ² x (0).     

Spatial extension of quantum gravitational particles inR 4×K N

It is observed that the magnitude relationma ² l _P/c holds if the non-Euclidean incremental spatial volume associated with a fundamental particle of massm and radiusa is characteristically quantum gravitational in a Kaluza-Klein or superstringR ⁴×K ^N . HereR ⁴ is the four-dimensional Riemannian space-time of general relativity andK ^N is a small-scale, compact,N-dimensional space of characteristic quantum gravitational volumel _P ^N , withl _P (G/c ³)^1/2= 1.61×10^–33 cm denoting the Planck length. For the electron and electron neutrino (assumed to possess nonzero mass bounded empirically by <30 eV) the derived magnitude relationa(l _P/mc)^1/2 yields the estimatesa _e 2.5×10^–22 cm and 3.3×10^–20 cm, spatial extensions which may be detectable by way of fine-scale effects in SSC experiments.     

AstrophysicalS(E) factor of10B(p, α1)7Be at low energies

The absolute cross section of the fusion reaction ¹⁰B(p, ₁)⁷ has been measured at the c.m. energy range E=48 to 159 keV via the 429 keV secondary -ray transition. The studies involved high proton currents and thick solid ¹⁰Btargets. The resulting cross sections have the same energy dependence as those of the ¹⁰B(p,₀)⁷Bereaction but they are lower by a factor 600.Supported in part by the Deutsche Forschungsgemeinschaft (Ro429/18-2 and Ro429/21-3), the Landesamt Nordrhein Westfalen (IVA5-10600387), and the Comision Intel-ministerial de Ciencia y Technologia (AEN90-0932).