Influence of the concentration of H₂–D₂ mixtures on their triple-point dewetting behavior

Triple-point dewetting of pure gases like hydrogen and deuterium on solid substrates is a well-known phenomenon. This property persists even for the mixed system of H₂ and D₂. There exists an effective triple-point temperature T₃⁽mix⁾ , between the T₃ of pure H₂ and the one of pure D₂, which depends on the species concentrations. We present new investigations for a wide range of H₂–D₂ concentrations measured under different thermodynamic conditions. This allows us to map out T₃⁽mix⁾ as function of concentration, which can be different in the melting or solidifying direction. Furthermore, it turns out that the time the system needs to reach an equilibrium state can be very long and depends on concentration. This is not observed for the pure H₂ and D₂ system. Sometimes the relaxation times are so extremely long that significant hysteresis occurs during ramping the temperature, even if this is done very slowly on a scale of hours. This behavior can be understood on the basis of mixing and demixing processes. Possible differences in the species concentrations in the gas, liquid, and especially solid phase of the system are discussed. A preliminary phase diagram of the H₂–D₂ system is established

Cooling System for a Superconducting DC-Rail

DC-rails are used in a wide field of industrial applications, for example in aluminum smelters and chlorine electrolysis plants. Up to now usually large sized DC-rails made out of copper or aluminum transport currents up to a few hundred kA. The development of compact, efficient and innovative superconductor components is forced mainly due to the high density of energy flux and requires a suitable cooling system. Replacing conventional high power rails to superconducting DC-rails allows a reduction in size, installation area and prize. Last but not least it will increase the electrical efficiency of the whole process. Within the framework of the government founded research project “3S-SupraStromSchiene”, project no. 03ET129C, a superconducting DC-rail was designed and is currently under construction. The ILK Dresden is responsible for the cooling system of this superconducting DC-rail. This novel cooling system that consists amongst others of a high power cryocooler and a special “cold” cryogenic pump will be presented for the use of a superconducting DC-rail system for a chloralkali process. The presentation describes the concept, design and experimental results of these key components. The high power cryocooler is based on the principle of a pulse tube cooler and provides a cooling power of 400 W at a temperature of 65 K. In ordinary pulse tube coolers the acoustic power at the warm end of the pulse tube is transformed to useless heat. Using two commercial reciprocating compressors, where one is acting as a compressor and the other one as expander, it is possible to recover a certain part of these acoustic power. In this way the theoretical efficiency exceeds 11% at 65 K. The cold cryogenic pump works fully submerged inside the subcooled liquid nitrogen reservoir and consists of a double acting piston pump which is powered by a linear drive. It provides a mass flow up to 0.5 kg/s at a pressure difference of up to 2 bar. Other parameters are possible depending on the design requirements

LHRH sparing therapy in patients with chemotherapy-naïve, mCRPC treated with abiraterone acetate plus prednisone: results of the randomized phase II SPARE trial

Background Although the benefit of androgen deprivation therapy (ADT) continuation in metastatic castration-resistant prostate cancer (mCRPC) remains controversial, clinical evidence is lacking. Recent results indicated that treatment with abiraterone acetate (AA) plus prednisone (P) further suppresses serum testosterone levels over ADT alone, suggesting that continuation of ADT in the treatment of mCRPC may not be necessary. Methods In this exploratory phase 2 study, mCRPC patients were randomized with a 1:1 ratio to receive either continued ADT plus AA + P (Arm A) or AA + P alone (Arm B). The primary endpoint was the rate of radiographic progression-free survival (rPFS) at month 12. Secondary endpoints included PSA-response rate, objective response, time to PSA progression and safety. Results A total of 68 patients were equally randomized between the two study arms. Median testosterone-levels remained below castrate-levels throughout treatment in all patients. According to the intention-to-treat analysis the rPFS rate was 0.84 in Arm A and 0.89 in Arm B. Moderate and severe treatment-emergent adverse events were reported for 72% of the patients in Arm A and for 85% of the patients in Arm B. Conclusions AA + P treatment without ADT may be effective in mCRPC patients and ADT may not be necessary in patients receiving AA + P

Triple-point wetting of molecular hydrogen isotopes

Triple-point wetting is a well-known phenomenon of simple adsorbates on solid substrates, which involves, in the liquid phase above the triple-point temperature, T3, complete wetting with the formation of arbitrary thick films being observed, whereas below T3 only a few monolayers of the solid phase are adsorbed at saturated vapour pressure. This effect is usually ascribed to the substrate-induced strain in the solid film, which occurs due to the lattice mismatch and the strong van der Waals pressure in the first few monolayers. Molecular hydrogen is a suitable system in which to investigate this phenomenon, in particular by tailoring the adsorbate substrate interaction by means of thin preplating layers of other adsorbates, and by introducing disorder into the system by using not only the pure systems H2 and D2, but also mixtures thereof. The experiments show that triple-point wetting is a rather dominant effect which, in contrast to expectations, persists even if the system parameters are widely varied. This indicates that the present understanding of this effect is incomplete. We present an investigation of the influence of the roughness of the substrate which is expected to be responsible for the dewetting of the solid phase

Triple-point wetting of molecular hydrogen isotopes

Triple-point wetting is a well-known phenomenon of simple adsorbates on solid substrates, which involves, in the liquid phase above the triple-point temperature, T3, complete wetting with the formation of arbitrary thick films being observed, whereas below T3 only a few monolayers of the solid phase are adsorbed at saturated vapour pressure. This effect is usually ascribed to the substrate-induced strain in the solid film, which occurs due to the lattice mismatch and the strong van der Waals pressure in the first few monolayers. Molecular hydrogen is a suitable system in which to investigate this phenomenon, in particular by tailoring the adsorbate–substrate interaction by means of thin preplating layers of other adsorbates, and by introducing disorder into the system by using not only the pure systems H2 and D2, but also mixtures thereof. The experiments show that triple-point wetting is a rather dominant effect which, in contrast to expectations, persists even if the system parameters are widely varied. This indicates that the present understanding of this effect is incomplete. We present an investigation of the influence of the roughness of the substrate which is expected to be responsible for the dewetting of the solid phase. 1

The growth of the non-wetting liquid 4He on Cs

It was theoretically predicted that the heavy alkali metals provide the only surfaces non-wetted by superfluid 4He below a certain temperature Tw. This was experimentally proven both for Cs and for Rb. However, investigations have shown that the non-wetting thin-film state for the He-Cs system is extremely dilute for T < Tw, yet close to Tw it can be much thicker and of the order of monolayers. Using the photoelectron tunneling method we have sensitively measured the growth of the non-wetting thin-film skate of 4He on a quench-condensed Cs surface. It turns out that far from coexistence there is little adsorption of helium. In contrast, close to GO-existence a rapid growth up to two to three monolayers of helium is observed, but the surface is still non-wet under the usual convention

The effect of electron pressure on suspended helium films

(Quasi) one- and zero-dimensional electron systems can be created using a suspended helium film on a structured substrate. To investigate the relation between the curved surface and the properties of the electron system, the suspended helium film profile in a quasi one-dimensional channel is measured interferometrically. It is shown that the film thickness decreases when the surface is charged with electrons at a density > 10 9 cm -2

Causes of Weak-localization of Electrons on Liquid Helium

We have investigated the dephasing processes in a weak localization (WL) experiment of a two-dimensional electron system on liquid helium. From low-field magnetoconductivity measurements we can separate the damping of WL on the dephasing of electrons due to electron-electron interaction and the motion of the helium vapour atoms. We observe an intermediate regime where both damping mechanisms are of comparable importance and determine the cross-over from one dominant regime to the other