Positron re-emission, reflection, and diffraction from W(100) surface at very low energies.

The energy distributions of scattered and re-emitted low-energy positrons from a W(100) surface were measured as a function of incident positron energy from 0 to 25 eV. Given that tungsten has a negative work function of about -3 eV for positrons, one can envisage three scenarios of very low-energy positron scattering from such a surface. First, a positron approaching the sample surface with energy say 1 eV above the vacuum level will see a potential barrier of about 2 eV height and will be reflected back to the vacuum. Second, when the energy of incident positrons increases up to the top of the surface potential barrier (positron work function), they start entering the solid and, therefore, the reflectivity of positrons from the surface reduces. Positrons entering the solid are thermalised within few picoseconds and have a chance to escape back to the vacuum with kinetic energy about 3 eV above the vacuum level undergoing so-calledre-emission. Third, coherent scattering of low-energy positrons may occur on the crystal surface, i.e. positron diffraction. All the three scenarios of low-energy positrons scattering are studied here experimentally. Measured spectra are very sensitive to the surface conditions of the sample: they change dramatically after surface oxidation or thin film deposition.

Smoking habits of UK military personnel on deployment: Exercise SAIF SAREEA 3.

INTRODUCTION: Changes of environment brought about by deployments are often attributed to an increase in smoking of service personnel. Electronic cigarettes are recognised as being a viable aid to quitting smoking but are currently banned from sale in Oman and were therefore banned during exercise SAIF SAREEA 3 (SS3). This paper sought to establish whether smoking increased on this exercise and for what reasons. Also, if deployed smoking cessation services are likely to be used, if available. METHODS: Questionnaires were distributed to deployed troops at various locations in theatre for data collection. RESULTS: Smoking prevalence increased by 5.2% (29) in the deployed population by the end of the exercise. The largest increase was seen in those smoking 20 cigarettes a day or more, rising by 269.8% (73) with a mean increase of 9 cigarettes per day. During the exercise the number of personnel using electronic cigarettes decreased and individuals' rate of electronic cigarette use also decreased. Those who smoked less during the exercise did mainly through choice (56.8%). 50% (280) of all individuals who increased smoking habits during the exercise did so out of boredom. CONCLUSIONS: During exercise SS3 the number of individuals who smoked and the quantity they smoked increased. The ban on electronic cigarettes in Oman and while on exercise potentially had an effect on the increased smoking habits. There is an argument to include smoking cessation material in medical modules to prevent ex-smokers from restarting, continue to aid those quitting and potentially lessen severity of increasing smoking habits while deployed.

Influence of polar groups in binary polymer blends on positronium formation.

The present work studied the role of the polar group unconjugated oxygen on the inhibition of positronium (Ps) formation in two binary blends made from a set of chosen constituent polymers with polar and weakly polar groups (nonpolar). The polymer blend samples of PVC-EVA and PVC-SAN were investigated by coincidence Doppler broadening and positron lifetime techniques. The strong polar acetate group in the EVA contributed to positron annihilation with electrons of unconjugated oxygen (-C(+)=O(-)) as revealed by the momentum distribution curves peaking around 17 P(L) (10(-3) m(0)c). The ortho-Ps intensity indicated the unconjugated oxygen shows about a 28% Ps reduction even in the presence of a strong Ps inhibiting halogen (Cl(-)). In contrast, this effect was not seen in the PVC-SAN blends since SAN contains a weakly polar (nonpolar) acrylonitrile group (C≡N). Our results indicate the chlorine of PVC in the blends is a major contributor to Ps inhibition through the formation of a (Cl(-)-e(+)) bound state but the unconjugated oxygen in EVA of the PVC-EVA blend also plays a similar, but lesser, role.

Auger-mediated sticking of positrons to surfaces: evidence for a single-step transition from a scattering state to a surface image potential bound state.

We present the observation of an efficient mechanism for positron sticking to surfaces termed here Auger-mediated sticking. In this process the energy associated with the positrons transition from an unbound scattering state to a bound image potential state is coupled to a valence electron which can then have sufficient energy to leave the surface. Compelling evidence for this mechanism is found in a narrow secondary electron peak observed at incident positron kinetic energies well below the electron work function.

Spatially resolved scanning probe electron energy spectroscopy for Ag islands on a graphite surface.

The scanning probe electron energy spectra for micron-sized Ag islands on highly ordered pyrolytic graphite substrate are measured. One- and two-dimensional relative intensity distributions for Ag or graphite plasmon peaks have been acquired and a lateral resolution of 4.8+/-2.4 microm has been achieved. It is the first time for the scanning probe electron energy spectroscopy technique to obtain the spatially resolved electron energy spectra with elemental contrast for a surface, which demonstrates the possibility of the element identification for the scanning tunneling microscope.

Miniature electrostatic electron energy analyzers and S-shaped deflector.

An instrument has been developed to avoid the rotation of large electron sources and detectors in quantum single particle scattering experiments. The rotation of an electron beam has been achieved by combining three small cylindrical electrostatic electron energy analyzers in series such that the first analyzer is fixed and the other two rotate together around the exit axis of the first; it is a development from an S-shaped deflector used by Hegemann et al. [J. Phys. B 26, 4607 (1993)]. Novel design and construction, using copper, aluminum, and stainless steel parts mounted on polyvinyl printed circuit board, enabled an efficient, small-sized high vacuum compatible instrument. The characteristics and versatility of the instrument have been shown by measurements of angular and spin asymmetries of electron scattering phenomena.

Endotoxin contamination in the dental surgery.

Dental waterlines contain large numbers of Gram-negative bacteria. Endotoxin, a component of such organisms, has significant health implications. Paired samples of dental unit water and the aerosols generated during dental procedures were collected, and assayed for bacteria and endotoxin levels, using heterotrophic plate counts and the Limulus amoebocyte lysate test. Consistent with published studies, the extent of bacterial contamination in the dental waters sampled for this investigation surpassed the levels associated with potable water, with counts in excess of 2.0x10(6) c.f.u. ml(-1) in some samples. Correspondingly high concentrations of endotoxin [up to 15 000 endotoxin units (EU) ml(-1)] were present in the water. A statistically significant Spearman correlation coefficient of rho=0.94 between endotoxin (EU ml(-1)) and bacterial load (c.f.u. ml(-1)) was demonstrated. All of the aerosol samples contained detectable endotoxin. Further studies of the consequences of dental endotoxin exposure, and evaluation of means to prevent exposure, are warranted.

Energy- and momentum-resolved exchange and spin-orbit interaction in cobalt film by spin-polarized two-electron spectroscopy.

Spontaneous ordering of electronic spins in ferromagnetic materials is one of the best known and most studied examples of quantum correlations. Exchange correlations are responsible for long range spin order and the spin-orbit interaction (SOI) can create preferred crystalline directions for the spins, i.e., magnetic anisotropy. Presented experimental data illustrate how novel spin-polarized two-electron spectroscopy in-reflection mode allows observation of the localization of spin-dependent interactions in energy-momentum space. Comparison of spin-orbit asymmetries in spectra of Co film and clean W(110) may indicate the presence of interface specific proximity effects providing important clues to the formation of preferred orientations for the magnetic moment of the Co film. These results may help to understand the microscopic origin of interface magnetic anisotropy.

Threshold electron-impact ionization mechanism for hydrogen atoms.

The near-threshold evolution of electron-impact ionization of hydrogen is revealed with measurements of the angular and energy correlations of the outgoing electrons down to 0.05 eV. The single-, double-, and triple-differential cross sections in the perpendicular plane are measured simultaneously using a dual wedge-and-strip detector on a single-toroidal energy analyzer, avoiding many experimental problems. The experimental and calculated data are in excellent agreement, within the experimental precision of +/-10%, and provide further evidence that the accurate solution of the Schrödinger equation provides a complete description of the reaction dynamics of near-threshold ionization.

Electron exchange in dissociative excitation of molecular hydrogen using polarized electrons.

The effects of electron exchange and spin orbit interaction in dissociative excitation processes in H2 molecules have been explored using excitation by polarized electrons. Observations of the circular and linear Stokes polarizations of the Balmer-alpha photons determined the alignment and orientation of the excited atomic hydrogen atoms, the excited molecular states, and the dissociative excitation processes via predissociation with short and long range transitions.

E1A-based determinants of oncogenicity in human adenovirus groups A and C.

A broad spectrum of genetic and molecular investigations carried out with group C, Ad2 and Ad5, and with group A, Ad12, have shown that early region1 (E1) gene products are sufficient for complete transformation of rodent cells in vitro by these viruses. During the past quarter century, the processes by which E1A proteins, in cooperation with E1B proteins, perturb the cell cycle and induce the transformed phenotype, have become well defined. Somewhat less understood is the basis for the differential oncogenicity of these two groups of viruses, and the processes by which the E1A proteins of Ad12 induce a tumorigenic phenotype in transformants resulting from infection of cells in vivo and in vitro. In this chapter we review previous findings and present new evidence which demonstrates that Ad12 E1A possesses two or more independent functions enabling it to induce tumors. One of these functions lies in its capacity to repress transcription of MHC class I genes, allowing the tumor cells to avoid lysis by cytotoxic T lymphocytes. We have shown that class I repression is mediated through increased binding of repressor COUP-TF and decreased binding of NF-kB to the class I enhancer. In addition to mediating immune escape, E1A also determines the susceptibility of transformants to Natural Killer (NK) cell lysis, and in this case, also, Ad12 transformants are not susceptible. By using Ad12 mutants containing chimeric E1A Ad12-Ad5 genes, point mutations, or a specific deletion, we have shown that the unique spacer region of Ad12 E1A is an oncogenic determinant, but is not required for transformation in vitro. Given that the E1A regions responsible for class I repression are first exon encoded, we have examined a set of cell lines transformed by these altered viruses, and have found that while they display greatly reduced tumorigenicity, they maintain a wildtype capacity to repress class I transcription. Whether the spacer contributes to NK evasion remains unresolved. Lastly, we discuss the properties of the Ad2/Ad5 E1A C-terminal negative modulator of tumorigenicity, and examine the effects on transformation, tumor induction and transformant tumorigenicity, when the Ad5 negative modulator is placed by chimeric construction in Ad12 E1A.

Mass spectrometric studies of the path of carbon in photosynthesis: positional isotopic analysis of (13)C-labelled C(4) to C(7) sugar phosphates.

The (EIMS) electron ionization mass spectrometric fragmentation patterns of the methoxime- and ethoxime-trimethylsilyl (TMS) derivatives of C(4) to C(7) sugars involved as phosphates in the Calvin pathway of photosynthesis in plants were analysed by gas chromatography/EIMS using specifically labelled (13)C analogs. In general, most but not all of the major ions in the mass spectra arise from single carbon-carbon bond cleavages of the straight-chain derivatives. The results confirm that GC/MS of the alkoxime-TMS derivatives is a viable method for measuring (13)C incorporations at individual carbon atoms in each of the sugar phosphates during photosynthetic experiments with (13)CO(2).

Detection of apoptosis in renal cell carcinoma.

Apoptosis is a selective process of programmed cell death that plays an important role in both physiologic and malignant states. In neoplastic disease, the rate at which a tumor grows depends on cell deletion as well as cell proliferation. It has been shown in several types of tumors that more aggressive tumors usually have a higher proliferative activity as well as an increased rate of apoptosis. The same characteristics seem true of renal neoplasms, as the frequency of apoptosis has been positively correlated with tumor grade, stage, and size in renal cell carcinoma (RCC) (1). Apoptosis is closely related to proliferative activity, tumor differentiation, and depth of invasion in transitional-cell carcinoma of the renal pelvis and ureter (2). The mechanisms of cell-cycle control, proliferation, and apoptosis are key issues in the biology and prognosis of RCCs. The expression of bcl-2 and p53 has been implicated in the control of apoptosis in tumorigenesis, and as a possible pathway to which cancer treatments could be directed. A reciprocal correlation was found between apoptosis and p53 positivity in RCC suggesting that the presence of mutant p53 is a negative regulator of apoptosis (3).

Infection-resistant nonleachable materials for urologic devices.

Bacterial colonization is the primary clinical problem faced by the surgeon and medical device innovator. Despite the absence of effective systemic treatment, medical implants and devices have been deployed with increasing success over the past five decades. Infection-resistant materials (IRMs) are a relatively recent addition to the science of implant and device development. The first IRM utilized leachable antimicrobial agents. Nonleachable technologies are being developed, some of which have the potential to make organ replacement even more successful in the future.

Treatment of androgen-independent prostate cancer using antimicrotubule agents docetaxel and estramustine in combination: an experimental study.

BACKGROUND: Estramustine in combination with other chemotherapeutic agents has demonstrated synergy in hormone-refractory prostate cancer. Docetaxel has demonstrated antineoplastic activity in a variety of chemotherapeutic-unresponsive tumors. We evaluated the effects of estramustine and docetaxel in preclinical models of prostate cancer. METHODS: Cell viability of PC-3 and MAT-LyLu (MLL) cells were assessed 48 hr after drug treatment. For in vivo studies, each flank of five animals in six groups was injected with 1 x 10(6) MLL cells: control, estramustine, docetaxel (low- and high-dose), and low- and high-dose docetaxel with estramustine. Animals were treated on days 4 and 11, and sacrificed on day 14. RESULTS: The IC(50) value for docetaxel was 2 nM in the PC-3 cells and 40 nM in the MLL cells. The addition of 100 nM of estramustine did not alter the IC(50) value for PC-3 cells. In the MLL cells, however, the IC(50) value was lowered to 15 nM. In vivo, low-dose docetaxel with estramustine demonstrated antineoplastic activity similar to that of high-dose docetaxel alone, suggesting additive activity between the drugs. CONCLUSIONS: These results demonstrate that when used in combination, docetaxel and estramustine can be more effective at lower dosages than when the individual drugs are used alone.

An immunoablative regimen of fludarabine and cyclophosphamide prevents fully MHC-mismatched murine marrow graft rejection independent of GVHD.

The prevention of graft rejection in the setting of nonmyeloablative transplant approaches might be mediated by chemotherapy-induced host immunoablation and by the graft-promoting effects of graft-versus-host disease (GVHD). To evaluate whether host immunoablation alone might allow for alloengraftment, we developed an F1-into-parent murine marrow rejection model using host preparative regimens of lethal total body irradiation (TBI; 950 cGy), sublethal irradiation (600 cGy), or combinations of fludarabine (Flu) and cyclophosphamide (Cy). A preparative regimen selectivity index (SI) was calculated to determine whether host lymphocytes were preferentially depleted relative to myeloid cells (SI = number of host myeloid/number host T lymphoid cells remaining after preparative regimen administration). Saline-treated recipients were assigned an SI value of 1.0. Recipients of lethal TBI had reduced myeloid cells relative to T cells (SI = 0.6). In contrast, all Flu/Cy regimens preferentially depleted host T cells: recipients of Flu (100 mg/kg per day)/Cy (50 mg/kg per day) for 10 days (SI = 28.1); recipients of Flu (100 mg/kg per day)/Cy (100 mg/kg per day) for 10 days (SI = 64.1); and recipients of Flu (100 mg/kg per day)/Cy (50 mg/kg per day) for 19 or 27 days (SI = 74.6). The 10-day regimen of Flu/Cy (50 mg/kg per day) did not severely reduce host T cell numbers, nor did it prevent F1 marrow rejection (<1% chimerism, n = 14). In contrast, the 10-day regimen of Flu/Cy (100 mg/kg per day) reduced T-cell numbers below that of lethal TBI recipients and prevented F1 marrow rejection (11.4% chimerism, n = 15); donor chimerism was predominant in lymphoid cells and was stable through day 240 post-BMT. Additionally, the 19- or 27-day regimen of Flu/Cy, which most selectively depleted host T cells, also prevented F1 marrow rejection (6.3% chimerism, n = 15). These results therefore demonstrate that optimized Flu-containing, immunoablative preparative regimens can prevent fully MHC-disparate marrow rejection independent of GVHD.

fas-mediated lysis of chronic lymphocytic leukaemia cells: role of type I versus type II cytokines and autologous fasL-expressing T cells.

Given the known role of the fas cytolytic pathway in B-cell regulation, we evaluated whether fas-fasL interactions might induce chronic lymphocytic leukaemia (CLL) cell death. De novo CLL cells expressed a low level of surface fas, and were not lysed by fasL-bearing cells. CLL cells cultured in media containing the type I cytokines interleukin (IL)-12 or interferon (IFN)-alpha had increased fas expression, and were readily lysed by fasL-bearing cells. In contrast, the type II cytokine IL-4 did not increase CLL cell fas, and abrogated type I cytokine-induced fas up-regulation. With prolonged culture, IL-4 exposed CLL cells expressed an intermediate level of fas; however, such CLL cells were resistant to fas-mediated lysis. These results indicate that IL-4 inhibits fas-mediated killing of CLL cells at the level of both fas receptor expression and post-receptor events. Additionally, we have defined in vitro culture conditions which generate fasL-bearing T cells from CLL patients; such T cells efficiently mediated fas-based lysis of autologous fas-positive CLL cells. We therefore conclude that type I and type II cytokines differentially regulate the fas pathway in CLL cells, and that a combination of type I cytokines and fasL-expressing T cells may represent a new approach to the immunotherapy of CLL.