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Notes: Scanning tunneling spectroscopy (STS) capable of measuring the local density of states dI/dV=G(V,x,y) correlated with the topography z(x,y) is implemented on a PC/AT computer system. An algorithm using dimensional decoupling and recursive linking is incorporated in a compact C-language code to achieve flexible and sophisticated STS control. Data acquisition and processing methods which provide the local density of states G(V,x,y,s) at different tip heights s in registry with z(x,y) are described. Examples of novel low-temperature experiments are given to show the capabilities of this implementation of STS.

Notes: We report on the spatially dependent enhanced etch rate of SiO2 in a CF4 planar reactive ion etcher due to the presence of the compounds GaAs or InP, or the single elements Ti, V, Nb, Ta, Cr, Mo, W, Ni, Pd, Pt, Cu, Ag, Au, Al, Ga, In, or Ge. The etch rate enhancement is maximum immediately adjacent to the source of the material and decreases nonlinearly with increasing distance away from the source of the material. Of the materials studied, the largest local etch rate increase was due to the element Ni (65% increase), followed closely by the elements In (57%) and Ga (43%) and the compounds InP (55%) and GaAs (40%). The lateral range of the effect extends 5 to 30 mm away from the material depending on the element or compound. Material interaction, possibly a catalized reaction, with the CF4 plasma reactants and lateral transport to provide an increased local concentration of fluorine at the SiO2 surface is a preliminary suggestion for the observed etch rate increase.

Notes: Electromigration failure of a series-parallel configuration of aluminum interconnects overlayed on tungsten contacts was measured using a novel multiple lognormal analysis. The analysis examined early failure mechanisms and allowed rapid determination of electromigration parameters on a statistically large number of junctions. The primary failure mode of these stuctures was complete migration of Al off of the W pads. This work suggested that Al/W metallizations, with a large number of series contacts, are prone to short mean time to failures.

Notes: The proximity-Josephson effect (PJE) is a powerful general method of determining the symmetry of the pair wave function in exotic superconductors. The method is simple and relatively insensitive to the surface condition of the sample. A superconducting probe (S) of known pairing symmetry (typically Nb or Ta) is brought into contact with the sample (N). Observations and arguments based on the de Gennes boundary condition at the NS interface both indicate formation of a local, proximity-induced superconducting region of depth ξ in the sample (N) under the probe. The induced pairs have the same symmetry as those of S. The expected pair-phase dependence of the coupling energy between the pairs in N and S leads to a Josephson current Ic(T), which may be observed up to a junction critical temperature T* which is typically ∼0.8 of the Tc of S. When the measurement temperature falls below the bulk Tc of N (the exotic superconductor), a pair wave function of possibly different symmetry forms in the bulk of N and overlaps the induced pair wave function near the probe. Weak interactions between the induced and bulk pairs occur. In the case of UBe13 contacted with a Ta tip, the interaction weakly suppresses the induced pairs [which determine Ic(T)] leading to a reduction of the Josephson current at T〈Tc. This observation of a negative S-wave proximity effect in superconducting UBe13, in good agreement with a Ginzburg–Landau analysis, is strong evidence for triplet pairing in this heavy fermion compound.

Notes: We describe a compact scanning tunneling microscope using piezoelectric bimorph elements to achieve a large scanning area of 20 μm2 at 4.2 K. This instrument provides inherent temperature compensation, compatibility with a high magnetic field environment, and a novel means of rough sample–tip (z) adjustment.

Notes: High quality etch masks for nanometer plasma processing can be formed from thin films of semimetallic amorphous carbon that are deposited by electron beam sublimation of graphitic carbon. These films are amorphous, hard, semimetallic, and mirror-reflective. These electron beam sublimation deposited (EBSD) semimetallic amorphous carbon (semimetallic a-C) thin films can be routinely deposited up to at least 400 nm thick and patterned by SF6 plasma reactive ion etching (RIE) via standard photoresist masks. They are demonstrated to be excellent etch masks on gallium arsenide, silicon, and germanium substrates using chemically assisted ion beam etching (CAIBE), also known as ion beam assisted etching (IBAE), reactive ion beam etching (RIBE), and RIE. The carbon etch masks have fine grain, low chemical reactivity, low sputter rates, and high thermal stability. Finally, the EBSD semimetallic a-C can be readily stripped by SF6 or O2 or H2 plasmas.

Notes: The mechanisms of embryo-maternal communication during the first days of embryonic life are largely unknown. Using the bovine as a model, the aims of our study were to morphologically characterize the interaction between the pre-implantation embryo and the epithelium of the maternal ampulla, isthmus and uterotubal junction by light and scanning electron microscopy. For this purpose, oviducts were removed from cows revealing a functional corpus luteum on day 3 after insemination. These were compared to oviducts removed on day 3 (metestrus) of the estrous cycle. Three days after insemination, the majority of the epithelial cells in the ampulla were secretory cells distinctly protruding into the oviductal lumen. Contrary the ampulla of cows on day 3 of the cycle predominantly revealed ciliated cells in the oviductal epithelium. As shown by Periodic Acid Schiff reaction (PAS) with and without amylase digestion, the secretory cells of the ampulla synthesized merely glycoproteins during metestrus, but large amounts of glycogen during pregnancy. In the isthmus no morphological differences were seen between pregnant and cyclic cows. The most conspicuous finding during pregnancy was seen in the uterotubal junction: Vital cumulus cells embedded in between epithelial cells had developed short cytoplasmic processes intensely contacting the epithelial uterine cells. The embryos obtained ex vivo were regularly covered with a thick layer of homogenous extracellular matrix. Contrary embryos produced in vitro– both with and without coculture with oviductal cells –revealed a clearly visible zona pellucida with spongy appearance and numerous pores. Our results imply that already during the first days of life there is intense interaction of the pre-implantation embryo and the maternal genital tract part of which may be mediated by cumulus cells.

Notes: Aims : Bone marrow is the major site of B-cell generation in humans. While in early childhood a high number of B-cell precursors is found in the bone marrow, only very few such cells are usually detectable in adult bone marrow. To assess the number of immature B cells present after haematopoietic cell transplantation the number of terminal deoxynucleotidyl transferase (TdT)-positive cells in regenerating bone marrow of adult patients was analysed.Methods and results : Bone marrow biopsy specimens were analysed from patients after allogeneic bone marrow transplantation (BMT; n = 14) or stem cell transplantation (SCT; n = 25) and autologous BMT (n = 9). Specimens from 11 untransplanted adult patients and 11 infants were also studied, as negative and positive controls, respectively. Immunohistochemistry was performed on paraffin-embedded bone marrow biopsy sections using TdT as a marker of lymphoid progenitors. Immunoreactivity for CD79a, CD20 and CD10 was used to confirm their B-cell origin. Using computer-assisted automated image analysis we quantitatively assessed the TdT+ cells present. We found a significant increase in the numbers of B-cell precursors in the bone marrow after allogeneic and autologous BMT/SCT compared with adult controls (P = 0.022). To analyse this in detail, we followed some patients after allogeneic BMT/SCT for up to 1445 days, when a marked B-cell increase was still detectable. However, the median number of TdT+ B cells after BMT/SCT was significantly lower than the number of equivalent B cells in infantile bone marrow biopsy specimens (P 〈 0.001).Conclusions : Bone marrow of adult patients after BMT/SCT is capable of initiating vigorous precursor B-cell generation, which is not seen in untransplanted adults. However, the increase of immature B cells was variable in our study. Only in two young adult patients did it reach the magnitude of B-cell generation seen in infantile bone marrow where immunocompetent B cells are produced normally. A marked increase in number of immature B cells post-transplant may mimic B-cell acute lymphoblastic leukaemia (B-ALL). This is a potential problem in patients transplanted for B-ALL itself. Since reactive and neoplastic B-cell precursors share the same immunophenotype in paraffin-embedded tissue, additional tools, particularly molecular techniques, may have to be employed to establish the correct diagnosis.

Notes: The effectiveness of synapses at various sites of the dendritic tree was studied using a segmental cable model with a program developed by Hines (Int. J. Biomed. Comput., 24, 55–68, 1989). The model rendered possible a high-fidelity simulation of the dendritic geometry of a frog motoneuron described in the accompanying paper (Birinyi et al., Eur. J. Neurosci., 1003–1012, 1992). The model was used in the passive membrane mode and the synaptic activity was simulated with current injections into large and small diameter dendrites at proximal and distal locations. Synaptic efficiency was defined by the charge transfer ratio expressed as the proportion of the injected current which appeared at the soma. The charge transfer ratio was determined with uniform and non-uniform distribution of specific membrane resistance over the soma–dendrite surface while the diameter of selected dendrite segments changed. The best charge transfer ratio was found with the largest dendrite membrane resistance, and the maximum efficiency of synaptic activity appeared at the original size of the dendrite segment stimulated. The amount of current that flowed in the proximal and distal directions from the segment stimulated depended on the diameter of that segment. The increase in diameter of proximal dendrites increased synaptic efficiency on distal dendrites, whereas the reverse caused a decline in synaptic efficiency on proximal dendrites. In addition to the diameter of dendrites, the arborization pattern also played a significant role in this mechanism. It is concluded that the cellulipetal increase in dendrite diameter greatly increases synaptic efficiency.