Keijsers, Shklyarevskii and van Kempen Reply

Answer to the Comment on ``Point-Contact Study of Fast and Slow Two-Level Fluctuators in Metallic Glasses'' by Jan von Delft et al.Comment: 3 pages, no figures, accepted Phys. Rev. Letter

Cellulose, een eindeloze bron van mogelijkheden

Vanwege de grote diversiteit van potentiële cellulose bronnen en de grote verschillen in kwalitatieve eigenschappen en samenstelling van deze cellulose types is het van belang in kaart te brengen voor welke toepassingen de verschillende grondstoffen het meest geschikt zijn. Voor het opstellen van een dergelijke “cellulose matrix” dient aandacht te zijn voor de kwalitatieve aspecten van de grondstof alsook voor de kwantitative beschikbaarheid en praktische verwerkbaarheid van de grondstof in de applicatie. WUR-FBR heeft tijdens deze initiële studie een gedetailleerde matrix opgesteld, waarbij de verschillende componenten van de matrix zijn geïdentificeerd en een eerste invulling van de matrix is opgezet

Transport properties and point contact spectra of Ni_xNb_{1-x} metallic glasses

Bulk resistivity and point contact spectra of Ni_xNb_{1-x} metallic glasses have been investigated as functions of temperature (0.3-300K) and magnetic field (0-12T). Metallic glasses in this family undergo a superconducting phase transition determined by the Nb concentration. When superconductivity was suppressed by a strong magnetic field, both the bulk sample R(T) and the point contact differential resistance curves of Ni_xNb_{1-x} showed logarithmic behavior at low energies, which is explained by a strong electron - "two level system" coupling. We studied the temperature, magnetic field and contact resistance dependence of Ni_{44}Nb_{56} point-contact spectra in the superconducting state and found telegraph-like fluctuations superimposed on superconducting characteristics. These R(V) characteristics are extremely sensitive detectors for slow relaxing "two level system" motion.Comment: 4 pages, 5 figure

Recurrent Pneumonia Due to an Appendiceal Mucinous Cystadenocarcinoma: A Rare Presentation of a Rare Malignancy

Mucinous cystadenocarcinoma of the appendix is a rare malignancy. This is a report of a 74-year-old man who presented with recurrent pneumonia which turned out to be a postobstructive pneumonia complicating a large mucinous cystadenocarcinoma of the appendix with massive retroperitoneal and intrathoracic extension. Mucinous cystadenocarcinoma of the appendix is a low-grade malignancy characterized by expansive growth due to progressive accumulation of mucinous fluid produced by the cancer cells. The tendency of this tumor to expand massively is well demonstrated by this case. The unusual retroperitoneal location of appendix in this patient probably allowed the tumor to expand massively in the retroperitoneal space and the thoracic cavity. In addition to computed tomography, [18F]fluorodeoxyglucose positron emission tomography (18F-FDG PET) was used as an ancillary method for staging in this patient. The value of 18F-FDG PET in the diagnosis of mucinous cystadenocarcinoma of the appendix has not been determined yet, but it might be promising. The most common presentation of this tumor is abdominal pain or a palpable ileocoecal mass. To the knowledge of the authors, this is the first report of an appendiceal mucinous cystadenocarcinoma with expansion into the thoracic cavity presenting with recurrent pneumonia

Transition from tunneling to direct contact in tungsten nanojunctions

We apply the mechanically controllable break junctions technique to investigate the transition from tunneling to direct contact in tungsten. This transition is quite different from that of other metals and is determined by the local electronic properties of the tungsten surface and the relief of the electrodes at the point of their closest proximity. The conductance traces show a rich variety of patterns from the avalanche-like jump to a mesoscopic contact to the completely smooth transition between direct contact and tunneling. Due to the occasional absence of an adhesive jump the conductance of the contact can be continuously monitored at ultra-small electrode separations. The conductance histograms of tungsten are either featureless or show two distinct peaks related to the sequential opening of spatially separated groups of conductance channels. The role of surface states of tungsten and their contribution to the junction conductance at sub-Angstrom electrode separations are discussed.Comment: 6 pages, 6 figure

Spin-Orbit-Induced Magnetic Anisotropy for Impurities in Metallic Samples II. Finite Size Dependence in the Kondo Resistivity

The electrical resistivity including the Kondo resistivity increase at low temperature is calculated for thin films of dilute magnetic alloys. Assuming that in the non-magnetic host the spin-orbit interaction is strong like in Au and Cu, the magnetic impurities have a surface anisotropy calculated in part I. That anisotropy hinders the motion of the spin. Including that anisotropy the effective electron-impurity coupling is calculated by using the second order renormalization group equations. The amplitude of the Kondo resistivity contribution is reduced as the position of the impurity approaches the surface but the increase occurs approximately at the bulk Kondo temperature. Different proximity effects observed by Giordano are also explained qualitatively where the films of magnetic alloys are covered by pure second films with different mean free path. The theory explains the experimental results in those cases where a considerable amount of impurities is at the surface inside the ballistic region.Comment: 39 pages, RevTeX (using epsfig), 15 eps figures included, submitted to PR

Orbital Kondo behavior from dynamical structural defects

The interaction between an atom moving in a model double-well potential and the conduction electrons is treated using renormalization group methods in next-to-leading logarithmic order. A large number of excited states is taken into account and the Kondo temperature $T_K$ is computed as a function of barrier parameters. We find that for special parameters $T_K$ can be close to $1 {\rm K}$ and it can be of the same order of magnitude as the renormalized splitting $\Delta$. However, in the perturbative regime we always find that T_K \alt \Delta with a T_K \alt 1 {\rm K} [Aleiner {\em et al.}, Phys. Rev. Lett. {\bf 86}, 2629 (2001)]. We also find that $\Delta$ remains unrenormalized at energies above the Debye frequency, $\omega_{\rm Debye}$.Comment: 9 pages, 9 figures, RevTe

Instability of the marginal commutative model of tunneling centers interacting with metallic environment: Role of the electron-hole symmetry breaking

The role of the electron-hole symmetry breaking is investigated for a symmetrical commutative two-level system in a metal using the multiplicative renormalization group in a straightforward way. The role of the symmetries of the model and the path integral technique are also discussed in detail. It is shown that the electron-hole symmetry breaking may make the model non-commutative and generate the assisted tunneling process which is, however, too small itself to drive the system into the vicinity of the two-channel Kondo fixed point. While these results are in qualitative agreement with those of Moustakas and Fisher (Phys. Rev. B 51, 6908 (1995), ibid 53, 4300 (1996)) the scaling equations turn out to be essentially different. We show that the main reason for this difference is that the procedure for the elimination of the high energy degrees of freedom used by Moustakas and Fisher leaves only the free energy invariant, however, the couplings generated are not connected to the dynamical properties in a straightforward way and should be interpreted with care. These latter results might have important consequences in other cases where the path integral technique is used to produce the scaling equations and calculate physical quantities.Comment: latex, figures in ps file adde