bluuebunny/crossref_metadata_2025 huggingface dataset:
Radial superlattices and single nanoreactors
Authors: Deneke Ch. , Jin-Phillipp N.-Y. , Loa I. , Schmidt O. G.
Published: May 2004

We investigate the wall structure and thermal stability of individual freestanding rolled-up nanotubes (RUNTs) using micro-Raman spectroscopy, transmission electron microscopy, and selected area electron diffraction. Our studies reveal that the walls of the InAs/GaAs RUNTs consist of a radial superlattice comprising alternating crystalline and noncrystalline layers. Furthermore, we locally heated individual RUNTs with a laser beam, and Raman spectroscopy was used in situ to monitor any structural changes. At about 300 °C the heated part of a RUNT starts to oxidize and eventually transforms into crystalline β-Ga2O3. This result shows that RUNTs can serve as nanoreactors that locally synthesize material at intentional places on a substrate surface.
Carbon nanotube-enhanced performance of microplasma devices
Authors: Park S.-J. , Eden J. G. , Park K.-H.
Published: May 2004

Incorporating multiwall carbon nanotubes (CNTs) directly into the cylindrical cathode of Ni screen/BN/Ni microplasma devices significantly improves all device performance parameters—operating and ignition voltages, as well as radiative efficiency. Having a cathode diameter of 200 μm, these devices exhibit operating voltages as much as 30 V (∼22%) lower than those required for an identical structure without CNTs. For Ne pressures of 100–300 Torr, ignition voltages are reduced by 14%–18% with the introduction of CNTs. In contrast, radiative efficiencies in the 300–800 nm spectral region are increased with CNTs by 6%–9% over the entire pressure range studied (200–600 Torr Ne). Voltage–current characteristics for two device configurations suggest that electrons generated within the cathode microcavity by CNT field emission are most effective in impacting device performance.
Correlated stacks of CdSe/ZnSSe quantum dots
Authors: Schmidt Th. , Clausen T. , Falta J. , Alexe G. , Passow T. , Hommel D. , Bernstorff S.
Published: May 2004

The observation and quantitative investigation of the spatial correlation of CdSe quantum dots in stacked CdSe/ZnSSe quantum-dot layers is reported. Using grazing incidence x-ray small angle scattering, the influence of the ZnSSe spacer layer thickness ranging from 20 to 80 Å, as well as the influence of the stacking number (3–10) has been analyzed. Satellite spots, indicative of quantum-dot ordering, have been observed for a spacer thickness of up to 45 Å, and for a stacking number of at least 5. This finding can be explained by a self-organized ordering process driven by the lattice mismatch induced strain. A mean lateral quantum-dot distance ranging from 116 to 145 Å, depending on the spacer thickness, has been found. In addition, an anisotropy of twofold symmetry has been observed, with the strongest correlation signal along 〈11̄0〉.
Photocurrent in ZnO nanowires grown from Au electrodes
Authors: Keem Kihyun , Kim Hyunsuk , Kim Gyu-Tae , Lee Jong Soo , Min Byungdon , Cho Kyoungah , Sung Man-Young , Kim Sangsig
Published: May 2004

ZnO nanowires were grown between two Au electrodes on an Al2O3-deposited Si wafer. Photoresponse, photoresponse spectrum, and current–voltage (I–V) studies were performed for the investigation into photoconduction mechanism in these nanowires. The photoresponse of the nanowires under the continuous illumination of light with above- or below-gap energies was slow, which indicates that photocurrent in the nanowires is surface-related rather than bulk-related. The photoresponse spectrum represents the above- and below-gap absorption bands for the photocurrents. The I–V characteristics under the illumination of the above-gap light are ohmic, but the characteristics under the illumination of the below-gap light are Schottky. This observation indicates that the above-gap light lowers the potential barrier built in the contact between the ZnO nanowires and electrodes, but that the below-gap light does not lower the potential barrier.
High-quality radio-frequency inductors on silicon using a hybrid ferrite technology
Authors: Saidani M. , Gijs M. A. M.
Published: May 2004

We have realized millimeter-size rf inductors on silicon using a polyimide mold–copper electroplating coil technology. Subsequently, the coils are assembled with magnetic cover plates of commercially available bulk Ni–Zn ferrites of high resistivity. Using the magnetic flux-amplifying ferrite plates, we obtain a 40% enhancement of the inductance and a 25% enhancement of the quality factor (Q=10–20) for frequencies up to 0.2 GHz. Our results indicate the large potential of using bulk ferrites for rf applications in a hybrid inductor assembly process.
Opposite effects of NO2 on electrical injection in porous silicon gas sensors
Authors: Gaburro Zeno , Oton Claudio J. , Pavesi Lorenzo , Pancheri Lucio
Published: May 2004

The electrical conductance of porous silicon fabricated with heavily doped p-type silicon is very sensitive to NO2. We show that the sign of the injection variations depends on the porous layer thickness. If the thickness is sufficiently low—of the order of few μm—the injection decreases instead of increasing. We discuss the effect in terms of an already proposed twofold action of NO2, according to which the free carrier density increases, and simultaneously the energy bands are bent at the porous silicon surface.
Dielectric characterization of Bi3.25La0.75Ti3O12 thin films
Authors: Wu Di , Li Aidong , Ming Naiben
Published: May 2004

Dielectric properties of Pt/Bi3.25La0.75Ti3O12(BLaT)/Pt ferroelectric thin film capacitors were studied as functions of frequency (40–106 Hz) and temperature (30–590 °C). BLaT thin films showed a first-order para-ferroelectric transition around 400 °C. Pt/BLaT/Pt capacitors post-annealed in Ar exhibited broadened transition with larger losses, which was interpreted in terms of increased oxygen vacancies. Via complex impedance spectroscopy study, the conduction activation energy of the space charges was determined to be ∼1.1 eV, close to that of oxygen vacancies in perovskite materials. The impedance characteristics of Pt/BLaT/Pt were compared with those of Pt/SrBi2Ta2O9(SBT)/Pt capacitors. The impact of dielectric characteristics on fatigue resistance of BLaT films was briefly discussed in comparison with SBT films.
All-organic dielectric-percolative three-component composite materials with high electromechanical response
Authors: Huang Cheng , Zhang Q. M. , deBotton Gal , Bhattacharya Kaushik
Published: May 2004

By combining the high-dielectric copper phthalocyanine oligomer (PolyCuPc) and conductive polyanline (PANI) within polyurethane (PU) matrix an all-organic three-component dielectric-percolative composite with high dielectric constant is demonstrated. In this three-component composite system, the high-dielectric-constant PolyCuPc particulates enhance the dielectric constant of the PU matrix and this combined two-component dielectric matrix in turn serves as the high-dielectric-constant host for the PANI to realize percolative phenomenon and further enhance the dielectric response. As a result, an electromechanical strain of 9.3% and elastic energy density of 0.4 J/cm3 under an electric field of 20 V/μm can be induced.
Enhancing the inscription rate of surface relief gratings with an incoherent assisting light beam
Authors: Yang Ke , Yang Suizhou , Wang Xiaogong , Kumar Jayant
Published: May 2004

A beam of light that is incoherent to the recording beams and has its polarization orthogonal to the recording beams is shown to assist the recording process of azo-functionalized polymers through the enhancement of trans–cis–trans cycling. Recording with s:s polarization has earlier been shown to result in very small surface modulations. However, with the help of an incoherent assisting beam, it can record a large surface modulation with a diffraction efficiency of 20.7%. The incoherent assisting beam also leads to an acceleration of the grating formation rate for the recording beams with p:p and 45°:45° polarization.
Introduction and control of metastable states in elliptical and rectangular magnetic nanoelements
Authors: Liu Xiaoxi , Chapman John N. , McVitie Stephen , Wilkinson Chris D. W.
Published: May 2004

Small elongated magnetic elements normally support near uniform magnetization distributions and switch abruptly under the influence of fields applied close to their long axes. However metastable states can be introduced in rectangular and elliptical nanoelements by applying fields parallel to their short axes. Using Lorentz microscopy and in situ magnetizing experiments we have established the conditions under which vortex states can be introduced. Their occurrence depends on the formation of a “C” rather than an “S” state as the applied field is reduced following saturation. Micromagnetic modeling provides support for the conclusions drawn from the experimental observations.
In-plane and out-of-plane band-gap properties of a two-dimensional triangular polymer-based void channel photonic crystal
Authors: Zhou Guangyong , Ventura Michael James , Straub Martin , Gu Min , Ono Atsushi , Kawata Satoshi , Wang Xuehua , Kivshar Yuri
Published: May 2004

The in-plane and out-of-plane band-gap properties of two-dimensional triangular void channel photonic crystals fabricated by femtosecond laser drilling in a solid polymer material were characterized for transverse electric (TE) and transverse magnetic (TM) polarization illumination. For a 24 layer structure stacked in the Γ–M direction, the fundamental stop gap resulted in the suppression of infrared transmission of as much as 96% for TE- and 85% for TM-polarized incident light. The midgap wavelength for the TM polarization was longer by 2.5% than that for the TE polarization. Increasing the angle of incidence for both the in-plane and out-of-plane cases shifted the stop gap to short wavelengths for both TE and TM polarizations. The experimental results allowed for the estimation of the cross section of void channels and the effective refractive index of the polymer after the fabrication.
Electrostatic micromembrane actuator arrays as motion generator
Authors: Wu X. T. , Hui J. , Young M. , Kayatta P. , Wong J. , Kennith D. , Zhe J. , Warde C.
Published: May 2004

A rigid-body motion generator based on an array of micromembrane actuators is described. Unlike previous microelectromechanical systems (MEMS) techniques, the architecture employs a large number (typically greater than 1000) of micron-sized (10–200 μm) membrane actuators to simultaneously generate the displacement of a large rigid body, such as a conventional optical mirror. For optical applications, the approach provides optical design freedom of MEMS mirrors by enabling large-aperture mirrors to be driven electrostatically by MEMS actuators. The micromembrane actuator arrays have been built using a stacked architecture similar to that employed in the Multiuser MEMS Process (MUMPS), and the motion transfer from the arrayed micron-sized actuators to macro-sized components was demonstrated.
Composition of Ge(Si) islands in the growth of Ge on Si(111)
Authors: Ratto Fulvio , Rosei Federico , Locatelli Andrea , Cherifi Salia , Fontana Stefano , Heun Stefan , Szkutnik Pierre-David , Sgarlata Anna , De Crescenzi Maurizio , Motta Nunzio
Published: May 2004

X-ray photoemission electron microscopy (XPEEM) is used to investigate the chemical composition of Ge/Si individual islands obtained by depositing Ge on Si(111) substrates in the temperature range 460–560 °C. We are able to correlate specific island shapes with a definite chemical contrast in XPEEM images, at each given temperature. In particular, strained triangular islands exhibit a Si surface content of 5%–20%, whereas it grows up to 30%–40% for “atoll-like” structures. The island’s stage of evolution is shown to be correlated with its surface composition. Finally, by plotting intensity contour maps, we find that island centers are rich in Si.
Omnidirectional resonance in a metal–dielectric–metal geometry
Authors: Shin Hocheol , Yanik Mehmet Fatih , Fan Shanhui , Zia Rashid , Brongersma Mark L.
Published: May 2004

We show that a planar metallic microcavity structure can exhibit an omnidirectional resonance, i.e., a resonance for which the resonance wavelength is independent of the incidence angle of light. The structure consists of a metal–dielectric–metal configuration. The omnidirectional resonance occurs when the reflection phase shift cancels the propagation shift. We numerically demonstrate such an omnidirectional resonance in an Ag–SiO2–Ag structure with realistic material parameters. Such omnidirectionally resonant structures are important for all-angle efficiency enhancement in light emitting diodes and photodetectors.
A route to diamond wafers by epitaxial deposition on silicon via iridium/yttria-stabilized zirconia buffer layers
Authors: Gsell S. , Bauer T. , Goldfuß J. , Schreck M. , Stritzker B.
Published: May 2004

A multilayer structure is presented which allows the deposition of high-quality heteroepitaxial diamond films on silicon. After pulsed-laser deposition of a thin yttria-stabilized zirconia (YSZ) layer on silicon, iridium was deposited by e-beam evaporation. Subsequently, diamond nucleation and growth was performed in a chemical vapor deposition setup. The epitaxial orientation relationship measured by x-ray diffraction is diamond(001)[110]∥Ir(001)[110]∥YSZ(001) [110]∥Si(001)[110]. The mosaicity of the diamond films is about an order of magnitude lower than for deposition directly on silicon without buffer layers and nearly reaches the values reported for single-crystal diamond on Ir/SrTiO3. In the effort towards single-crystal diamond wafers, the present solution offers advantages over alternative growth substrates like large-area oxide single crystals due to the low thermal expansion mismatch.
Optical properties of heterodiamond B2CN using first-principles calculations
Authors: Sun Jian , Wang Hui-Tian , Ming Nai-Ben , He Julong , Tian Yongjun
Published: May 2004

We report detailed ab initio calculations of the optical properties of a heterodiamond B2CN compound using the pseudopotential density functional method, including the dielectric function, the refractive index, the absorption, the electron energy-loss spectrum, and the reflectivity. The polarization dependencies of those optical properties are investigated. The results indicate that the electron-deficiency characteristic of B2CN gives rise to some features.
Atomic-scale observation of interfacial roughness and As–P exchange in InGaAs/InP multiple quantum wells
Authors: Yamakawa I. , Oga R. , Fujiwara Y. , Takeda Y. , Nakamura A.
Published: May 2004

Cross-sectional scanning tunneling microscopy (XSTM) has been used to study interfacial properties of InP-on-InGaAs interfaces in InGaAs/InP multiple quantum wells grown by metalorganic vapor phase epitaxy with a growth interruption. XSTM has enabled us to separately identify step-like roughness and distributions of As atoms incorporated in the InP layer near the interface. The As composition profile along the growth direction analyzed from distributions of As atoms in XSTM images shows an exponential variation with distance from the InP-on-InGaAs interface. It is found that the growth interruption of 30 s reduces considerably the roughness amplitude to 0.45 nm from 1.1 nm and increases the coherent length from 22 to 27 nm.
Influence of pulse duration on the amorphization of GeSb thin films under ultrashort laser pulses
Authors: Wiggins S. M. , Solis J. , Afonso C. N.
Published: May 2004

Laser-induced amorphization of crystalline, 25-nm-thick, Sb-rich GeSb films has been studied for pump pulse durations in the range from 100 fs up to 6 ns. The dynamics of the phase change has been investigated using real-time reflectivity measurements with picosecond time resolution performed with a streak camera. For pulses in the femtosecond regime, the time required to complete the transformation is of the order of ∼10–15 ns. When the pulse duration is increased to the 1.5–20 ps range, the transformation time decreases to values as short as 400 ps, while for nanosecond laser pulses amorphization is not achievable. This behavior is discussed in terms of the heat flow dynamics of the system and the influence of pulse duration on the initial supercooling and nucleation rate.
Crystal nucleation and growth processes in Ge2Sb2Te5
Authors: Privitera S. , Bongiorno C. , Rimini E. , Zonca R.
Published: May 2004

The kinetics of the amorphous-to-crystal transition in Ge2Sb2Te5 thin films have been studied through in situ transmission electron microscopy analyses. By following the time evolution of the grain density and size, the growth velocity and the nucleation rate have been separately measured at different annealing temperatures. Activation energies of 2.9±0.5 eV and 2.3±0.4 eV have been obtained for the nucleation rate and the growth velocity, respectively. The barrier energy for the nucleation of a critical nucleus ΔG* has been evaluated, and the scalability of phase change nonvolatile memories has been estimated.
Stable extremely-high-damping discrete viscoelastic systems due to negative stiffness elements
Authors: Wang Yun-Che , Lakes Roderic S.
Published: May 2004

Systems with negative stiffness constituents can have extreme material properties greatly exceeding those of either constituent. We show that a discrete system with a viscoelastic damping element and a negative stiffness element can be made with overall viscoelastic damping orders of magnitude higher than that of any constituent, or of the system with all elements of positive stiffness. The product of stiffness and damping, important for vibration damping, is also enhanced by orders of magnitude. We show this system is unconditionally stable in the high damping regime. The singularity in damping can be made arbitrarily close to the stability boundary.
Spatially periodic structures, under femtosecond pulsed excitation of crystals
Authors: Martynovitch Evgueni F. , Petite Guillaume , Dresvianski Vladimir P. , Starchenko Anton A.
Published: May 2004

Measuring the luminescence intensity of specially prepared irradiation defects induced in crystals, we observe that the longitudinal structure of quasi-interferences induced by two orthogonally polarized femtosecond pulses propagating together with different velocities is insensitive to the spatial broadening due to velocity dispersion in the crystals. On the contrary, it does depend on the pulse duration when it is changed by varying the spectral width of the radiation. It thus allows a direct measurement of the coherence time of such pulses. Stability of the axial selectivity is a good sign, taking away a number of serious limitations concerning possible applications.
Polarity control of ZnO on sapphire by varying the MgO buffer layer thickness
Authors: Kato Hiroyuki , Miyamoto Kazuhiro , Sano Michihiro , Yao Takafumi
Published: May 2004

Polarity-controlled ZnO films with an MgO buffer layer were grown on c-plane sapphire by plasma-assisted molecular-beam epitaxy. Convergent beam electron diffraction results showed that Zn-polarity (+c) growth occurred when the MgO layer was thicker than 3 nm, whereas O-polarity (−c) growth occurred when the layer was less than 2 nm. Reflection high-energy electron diffraction results revealed that MgO growth was Stranski–Krastanov mode, and that the growth mode transition from two- to three-dimensional occurred when the layer was thicker than 1 nm. In conclusion, polarity conversion apparently occurs due to the different atomic structure between the wetting layer and islands of MgO.
ELECTRON DENSITOMETRY OF STAINED VIRUS PARTICLES
Authors: Hall Cecil E.
Published: May 2004

Methods are described for determining the relative mass of particles in electron microscope specimens through the measurement of photographic densities in recorded images. These methods were applied to a quantitative study of the amounts of electron stains that could be associated with the particles of tomato bushy stunt virus (BSV) and tobacco mosaic virus (TMV). In the pH range above 2 where the viruses are stable, the amount of stain absorbed is too small to produce adequate contrast in the electron microscope. Maximum stain absorption was achieved at pH about 1 where with several reagents and combinations of reagents the mass of BSV could be increased to about four times that of the unstained particles. Optimum results were obtained with phosphotungstic acid alone or in combination with Pt, Th, or La ions. Since the pH conditions for high stain absorption are normally destructive, morphology is satisfactorily preserved only when the phosphotungstic acid is applied in concentrations of 10 per cent or greater or when the use of destructive reagents is preceded by a preliminary fixation under mild conditions. Maximum staining of TMV increased the mass of the particles to about two times that of the unstained.

Estimates of the mass of heavily stained BSV particles indicate that their density is 3.3 gm./cm.3 The high internal hydration of BSV probably accounts for the greater stain absorption and penetration compared to those of TMV which has very low or zero internal hydration.

Anomalous images resulting from the use of electron stains are shown and discussed.
A MICROPHOTOMETRIC STUDY OF THE SYNTHESES OF DESOXYRIBONUCLEIC ACID AND NUCLEAR HISTONE
Authors: Bloch David P. , Godman Gabriel C.
Published: May 2004

1. The fast green stain of Alfert and Geschwind for nuclear basic protein is shown to obey the Beer-Lambert laws when used on purified histone. Interference from acid substances other than nucleic acids as a possible source of error is indicated.

2. Use of this technique after a modified Feulgen stain enables determination of relative amounts of desoxyribonucleic acid and histone in the same individual cells.

3. DNA and histone are shown to have the same distribution in formalin-fixed nuclei.

4. The syntheses of DNA and histone proceed simultaneously resulting in the doubling of both these substances prior to cell division.

5. The standard error for histone values is greater than that for DNA; however, the source of this variability is not known.
A SMALL PARTICULATE COMPONENT OF THE CYTOPLASM
Authors: Palade George E.
Published: May 2004

A particulate component of small dimensions (100 to 150 A) and high density is described in the ground substance of the cytoplasm of mammalian and avian cells.

In many cell types that seem to have in common a high degree of differentiation, the new component is preferentially associated with the membrane of the endoplasmic reticulum; whereas in other cell types, characterized by rapid proliferation, it occurs more or less freely distributed in the ground substance of the cytoplasm.

In the Discussion an attempt is made to integrate the observations presented in this paper with the already available cytological, histochemical, and cytochemical information.
THE FINE STRUCTURE OF NEURONS
Authors: Palay Sanford L. , Palade George E.
Published: May 2004

1. Thin sections of representative neurons from intramural, sympathetic and dorsal root ganglia, medulla oblongata, and cerebellar cortex were studied with the aid of the electron microscope.

2. The Nissl substance of these neurons consists of masses of endoplasmic reticulum showing various degrees of orientation; upon and between the cisternae, tubules, and vesicles of the reticulum lie clusters of punctate granules, 10 to 30 mµ in diameter.

3. A second system of membranes can be distinguished from the endoplasmic reticulum of the Nissl bodies by shallower and more tightly packed cisternae and by absence of granules. Intermediate forms between the two membranous systems have been found.

4. The cytoplasm between Nissl bodies contains numerous mitochondria, rounded lipid inclusions, and fine filaments.
THE USE OF SILVER NITRATE AS A VITAL STAIN, AND ITS DISTRIBUTION IN SEVERAL MAMMALIAN TISSUES AS STUDIED WITH THE ELECTRON MICROSCOPE
Authors: Dempsey Edward W. , Wislocki George B.
Published: May 2004

After chronic administration of a dilute solution of silver nitrate in drinking water to rats, mice, and guinea pigs, granular deposits of metallic silver were detected in electron micrographs of the kidney, liver, thyroid, and pancreas. The silver deposits were in the form of extremely dense, angular particles with sharp outlines. They varied from aggregates a few microns in diameter down to granules at the limit of resolution of the electron microscope.

The principal sites of deposition were (1) basement membranes, especially those of the renal glomeruli, proximal convoluted tubules, and various glands, and those associated with vascular endothelium, and (2) the cytoplasm of fixed and free macrophages. Both in Kupffer cells lining hepatic sinusoids and in the wandering macrophages of other tissues, the silver was segregated in discrete vacuoles. In addition, granular deposits were observed in occasional vesicular structures in the proximal convoluted tubules of the kidney, the hepatic cells, and the pancreatic acinar cell. These structures, in favorable preparations, contained an outer double layered membrane and internal folds similar to those of mitochondria, from which they appear to have been derived. The significance of these findings in heavy metal poisoning and in cellular physiology is briefly discussed.
FACTORS INFLUENCING THE ABILITY OF ISOLATED CELL NUCLEI TO FORM GELS IN DILUTE ALKALI
Authors: Dounce Alexander L. , Monty Kenneth J.
Published: May 2004

1. Known methods for isolating cell nuclei are divided into two classes, depending on whether or not the nuclei are capable of forming gels in dilute alkali or strong saline solutions. Methods which produce nuclei that can form gels apparently prevent the action of an intramitochondrial enzyme capable of destroying the gel-forming capacity of the nuclei. Methods in the other class are believed to permit this enzyme to act on the nuclei during the isolation procedure, causing detachment of DNA from some nuclear constituent (probably protein).

2. It is shown that heating in alkaline solution and x-irradiation can destroy nuclear gels. Heating in acid or neutral solutions can destroy the capacity of isolated nuclei to form gels.

3. Chemical and biological evidence is summarized in favor of the hypothesis that DNA is normally bound firmly to some nuclear component by non-ionic linkages.
SEDIMENTATION AND VISCOSITY STUDIES ON THE CAPSULAR AND SOMATIC POLYSACCHARIDES OF PNEUMOCOCCUS TYPE III
Authors: Koenig Virgil L. , Perrings J. D.
Published: May 2004

Sedimentation constants at infinite dilution have been found to be 1.89 and 4.06 for the somatic and capsular polysaccharides, respectively, from pneumococcus Type III.

Intrinsic viscosities have been determined for the somatic and capsular polysaccharides of pneumococcus Type III using the Ostwald viscometer.

Molecular weights and dimensions have been calculated for the somatic and capsular polysaccharides of pneumococcus Type III assuming the molecules to be prolate ellipsoids of revolution. Values for the somatic polysaccharide are: molecular weight, 26,400; diameter, 0.97 mµ; and length, 36.18 mµ. Values for the capsular polysaccharide are: molecular weight, 171,800; diameter, 1.04 mµ; and length, 177.87 mµ.

The molecular weights were calculated for the somatic and capsular polysaccharides of pneumococcus Type III assuming the molecules to be flexible chains. The value of the molecular weight of the somatic polysaccharide is 31,500 and the value for the molecular weight of the capsular polysaccharide is 267,500.

The molecules of both the somatic and capsular polysaccharides exhibit high degrees of asymmetry.
THE MACROMOLECULAR PARACRYSTALLINE LATTICE OF INSECT VIRAL POLYHEDRAL BODIES DEMONSTRATED IN ULTRATHIN SECTIONS EXAMINED IN THE ELECTRON MICROSCOPE
Authors: Morgan Councilman , Bergold G. H. , Moore Dan H. , Rose Harry M.
Published: May 2004

Thin sections of polyhedra obtained from gipsy moth larvae infected with P. dispar virus and from silkworm larvae infected with B. mori virus revealed viral particles contained within a pseudohexagonal, macromolecular, paracrystalline lattice. The gipsy moth virus occurs in bundles of one to eight rods enclosed by a limiting membrane. The particles of the silkworm virus, although generally occurring singly, also possess a limiting membrane. The macromolecules appear to be dense, discrete particles when cross-sectioned and to form dense bands by superimposition when longitudinally or obliquely sectioned at certain angles. Calculations of macromolecular size have been made.
ELECTRON MICROSCOPE STUDIES ON THE CELLS OF THE MALPIGHIAN TUBULES OF THE GRASSHOPPER (ORTHOPTERA, ACRIDIDAE)
Authors: Beams H. W. , Tahmisian T. N. , Devine R. L.
Published: May 2004

For purposes of description, the cells of the Malpighian tubules of the grasshopper may be divided into basal, intermediate, and apical zones.

The basal zone of the cell contains what appears to be an elaborate infolding of the cell membrane at the base. This condition results in the basal cell cytoplasm being divided into many compartments. The compartments contain mitochondria that are often arranged in rows. Other small bodies which possess relatively dense outer borders and less dense cores were observed within the compartments. These bodies are unidentified.

The brush border of the apical zone contains a multitude of vertically arranged protoplasmic processes. Stages were found which suggest that the filamentous mitochondria migrate from the cell body to the base of the protoplasmic processes, where they enter them and move apically. Some of the mitochondria were observed at the very tips of the processes where they enlarge producing an accompanying bulging of the tips. This condition is interpreted as a stage in the pinching off of the mitochondria-laden tips of the protoplasmic processes.
OPTICAL ROTATION AND HELICAL POLYPEPTIDE CHAIN CONFIGURATION IN COLLAGEN AND GELATIN
Authors: Cohen Carolyn
Published: May 2004

The optical rotation phenomena exhibited by a citrate-extracted fraction of ichthyocol (from carp swim bladder), as well as by the parent gelatin derived therefrom, have been studied. Dispersion data for all cases follow a single-term Drude equation, but the variations with state are adequately expressed by simple reference to changes in [α]D as follows:—

1. The native collagen fraction, dispersed in 0.15 M citrate buffer at pH 3.7 in the cold (11°C.), yields a high negative specific rotation, [α]D, near –350°.

2. During equilibration at 40°C., which causes conversion to a monodisperse parent gelatin, the rotation drops to about –110°.

3. Gelation at 2°C. results in a partial regain of rotation to around –290°. This mutarotation is reversible, depending on temperature.

4. In the range 0.02 to 0.28 per cent the native ichthyocol and the warm gelatin solutions show little concentration dependence, but with the cold gelatin solutions the specific rotation increases with concentration. Gelatin films formed by cold evaporation yield high specific rotation (ca. –620°), but those formed by hot evaporation retain low optical activity.

5. Since this same collagen-gelatin system has been investigated physicochemically, it is possible to relate molecular changes to the observed variations in optical rotation. Conclusions are similar to those of Robinson (1953), who studied other gelatins: high negative rotation is believed related to a native collagen polypeptide configuration, herein specified as helical (from x-ray diffraction considerations) and destroyed by heating. The possible roles of intermolecular interactions and of prevalent pyrrolidine constituents in influencing the helical configuration and optical activity are discussed.
TWO PROTEINS PURIFIED FROM LOBSTER NERVE EXTRACT
Authors: Maxfield Myles , Hartley Robert W.
Published: May 2004

1. A protein component, fraction B, of lobster nerve extracts has been isolated and purified by differential ultracentrifugation and precipitation with zinc acetate.

2. Physicochemical data obtained from this protein and from fraction C are summarized.

3. Fraction B is present in lobster nerve extracts in higher concentration (relative to fraction A) than in blood.

4. A second component, fraction C, of sedimentation constant S20o = 13.2 has been isolated from lobster nerve extracts.
STUDIES ON THE FINE STRUCTURE OF THE MAMMALIAN TESTIS
Authors: Burgos Mario H. , Fawcett Don W.
Published: May 2004

The differentiation of cat spermatids was studied in thin sections examined with the electron microscope. The Golgi complex of the spermatid consists of a central aggregation of minute vacuoles, partially surrounded by a lamellar arrangement of flattened vesicles. In the formation of the acrosome, one or more moderately dense homogeneous granules arise within vacuoles of the Golgi complex. The coalescence of these vacuoles and their contained granules gives rise to a single acrosomal granule within a sizable membrane-limited vacuole, termed the acrosomal vesicle. This adheres to the nuclear membrane and later becomes closely applied to the anterior two-thirds of the elongating nucleus to form a closed bilaminar head cap. The substance of the acrosomal granule occupies the narrow cleft between the membranous layers of the cap.

The caudal sheath is comprised of many straight filaments extending backward from a ring which encircles the nucleus at the posterior margin of the head cap.

Attention is directed to the frequent occurrence of pairs of spermatids joined by a protoplasmic bridge and the origin and possible significance of this relationship are discussed.
INTERPRETATIONS OF ELECTRON MICROGRAPHS OF SINGLE AND SERIAL SECTIONS
Authors: Williams Robley C. , Kallman Frances
Published: May 2004

A method of securing serial sections for electron microscopy is described. Serial sections present certain anomalies of interpretation of a nature such that a complete and detailed three-dimensional reconstruction of the sectioned tissue cannot be made. These anomalies are discussed, as well as those which have been encountered in the interpretation of single sections. Observations of the following kinds have been made in an attempt to elucidate the interpretation of single and serial sections: differing methods of mounting adjacent sections, observation of the same section by high-angle stereoscopy, and examination of sections which have been shadowed prior to and subsequent to electron microscopy.

It is found that the appearance of sections is independent of the choice of side to be placed against the formvar films. Stereoscopy shows that the appearance of fine structures is strongly dependent upon the direction of the penetrating electron beam with respect to the plane of the structures. Stereoscopy, combined with shadowing, shows quantitatively that extensive sublimation of polymer occurs upon normal exposure in the electron microscope. Observation of sections shadowed prior to electron microscopy indicates that varying amounts of material are removed between sections by the action of microtomy; i.e., it is probable that the sum of the thicknesses of several serial sections is considerably less than the total thickness of material removed from the block. It is believed that this effect, combined with the effect of sublimation, aids in explaining the failure of adjacent sections to exhibit continuity in their detailed structures.
STUDIES OF TWO TYPES OF ALKALINE PHOSPHATASE IN NUCLEI ISOLATED FROM THE LIVERS OF FED AND FASTED RATS BY A MODIFICATION OF THE BEHRENS TECHNIQUE
Authors: Emery Arthur J. , Dounce Alexander L.
Published: May 2004

1. Rat liver nuclei were isolated from normal rats and rats fasted for 36 hours by a slight modification of the Behrens technique.

2. The nucleus of the rat liver cell contains two types of alkaline phosphatase. This confirms the previous findings on rat liver nuclei isolated in aqueous media.

3. The one type of alkaline phosphatase is not activated by magnesium ions, and this enzyme is very strongly bound to structural material of the nucleus. The other type of alkaline phosphatase is activated by magnesium ions, and this enzyme is probably free to diffuse from cytoplasm to nucleus and vice versa through the nuclear membrane.

4. Fasting caused a pronounced decrease of protein in general and of the alkaline phosphatase which is activated by magnesium ions from the nucleus of the rat liver cell, while the alkaline phosphatase that is not activated by magnesium was less affected.
ON ARTIFACTS APPEARING IN THE HISTOCHEMICAL FIXATION OF GLYCOGEN
Authors: Takahashi Kohnosuke , Iwase Shoji
Published: May 2004

1. Fixation artifacts associated with glycogen translocation are prevalent in tissues of parenchymatous type and scarce or non-existent in tissues of loose type.

2. Liver tissue treated with M/3 NaOH solution before fixation did not show an uneven distribution of glycogen. This was interpreted as indicating that the liver, a tissue of parenchymatous type, was changed, so to speak, into a loose type of tissue by alkali treatment.

3. The so called Alkohol-flucht of glycogen was produced in Yoshida's ascites tumor cells by a procedure which changed a loose type of tissue into a parenchymatous one, that is, by packing the tumor cells tightly.

4. The translocation of glycogen in cells appeared to occur when the fixatives penetrated the cells rapidly from a single direction, but failed to occur when the cells were attacked by the fixative from all directions.

5. In dried smears of Yoshida's ascites tumor cells and bone marrow cells, the glycogen particles are translocated to the peripheral regions of the cells, and coalesce there.

The production of these artifacts is related in some way to the physicochemical properties of the protoplasm and plasma membrane of the cells.
OBSERVATIONS ON THE FINE STRUCTURE OF THE MACRONUCLEUS OF TOKOPHRYA INFUSIONUM
Authors: Rudzinska Maria A. , Porter Keith R.
Published: May 2004

The macronucleus in Tokophrya infusionum is composed of numerous Feulgen-positive chromatin bodies (about 0.5 µ in diameter) which appear in thin sections as a dense spongework, homogeneous throughout. The same appearance characterizes metaphase chromosomes of higher forms.

Some chromatin bodies of the macronucleus were found to possess a highly organized structure in certain old organisms. This structure appears in cross-sections as a honeycomb and in longitudinal sections as parallel lines about 120 A in diameter evenly spaced (about 230 A).

As far as is known this is the first time a regular structure has been found in bodies of chromosomal character at the dimensional level presently explored by electron microscopy. The demonstration that OsO4 can preserve order in chromatin material is another significant aspect of these findings.
THE FINE STRUCTURE OF THE GALL BLADDER EPITHELIUM OF THE MOUSE
Authors: Yamada Eichi
Published: May 2004

Sections of mouse gall bladder epithelium fixed by perfusion with buffered osmium tetroxide have been studied in the electron microscope as an example of simple columnar epithelium.

The free surface presents many microvilli, each presenting a dense tip, the capitulum, and displaying a radiating corona of delicate filaments, the antennulae microvillares. Very small pit-like depressions, representing caveolae intracellulares, are encountered along the cell membrane of the microvilli.

The free cell surface between microvilli shows larger cave-like depressions, likewise representing caveolae intracellulares, containing a dense material.

The lateral cell borders are extensively folded into pleats, which do not interdigitate extensively with corresponding folds of the adjacent cell membrane.

The terminal bars are shown to consist of thickened densities of the cell membrane itself in the region of insertion of the lateral cell wall with the free cell surface. This thickening is associated with an accumulation of dense cytoplasmic material in the immediate vicinity. The terminal bar is thus largely a cytoplasmic and cell membrane structure, rather than being primarily intercellular in nature.

The basal cell membrane is relatively straight except for a conical eminence near the center of the cell, projecting slightly into the underlying tunica propria. The basal cell membrane itself is overlain by a delicate limiting membrane, which does not follow the lateral contours of the cell.

Unmyelinated intercellular nerve terminals with synaptic vesicles have been encountered between the lateral walls of epithelial cells.

A division of the gall bladder epithelial cell into five zones according to Ferner has been found to be convenient for this study.

The following cytoplasmic components have been noted, and their distribution and appearance described: dense absorption granules, mitochondria, Golgi or agranular membranes, endoplasmic reticulum or ergastoplasm, ring figures, and irregular dense bodies, perhaps lipoid in nature. The nucleus of these cells is also described.
A NEW FREEZING-ULTRAMICROTOME
Authors: Moor H. , Mühlethaler K. , Waldner H. , Frey-Wyssling A.
Published: May 2004

The difficulties in sectioning frozen biological objects for electron microscopic investigations are overcome by Steere's freezing-etching method. In order to test this method and to open up a wide field of application, the new freezing-ultramicrotome has been designed. The apparatus consists of the combination of an ultramicrotome with freezing-drying and shadow-casting installations in the same vacuum container. The preliminary results show, on the one hand, the practicability of all preparational steps and, on the other, that it is possible to resolve internal structures of cell organelles and even macromolecular patterns.
ANGULAR LIGHT-SCATTERING STUDIES ON ISOLATED MITOCHONDRIA
Authors: Gotterer Gerald S. , Thompson Thomas E. , Lehninger Albert L.
Published: May 2004

Angular light-scattering studies have been carried out on suspensions of isolated rat liver mitochondria. The angular scatter pattern has a large forward component, typical of large particles. Changes in dissymmetry and in the intensity of light scattered at 90° have been correlated with changes in optical density during the course of mitochondrial swelling and contraction. Such changes can be measured at mitochondrial concentrations much below those required for optical density measurements. Changes in mitochondrial geometry caused by factors "leaking" from mitochondria, not detectable by optical density measurements, have been demonstrated by measuring changes in dissymmetry. Angular light-scattering measurements therefore offer the advantages of increased sensitivity and of added indices of changes in mitochondrial conformation.
CENTRIOLE REPLICATION
Authors: Gall Joseph G.
Published: May 2004

This paper describes the replication of centrioles during spermatogenesis in the Prosobranch snail, Viviparus malleatus Reeve. Sections for electron microscopy were cut from pieces of testis fixed in OsO4 and embedded in the polyester resin Vestopal W. Two kinds of spermatocytes are present. These give rise to typical uniflagellate sperm carrying the haploid number of 9 chromosomes, and atypical multiflagellate sperm with only one chromosome. Two centrioles are present in the youngest typical spermatocyte. Each is a hollow cylinder about 160 mµ in diameter and 330 mµ long. The wall consists of 9 sets of triplet fibers arranged in a characteristic pattern. Sometime before pachytene an immature centriole, or procentriole as it will be called, appears next to each of the mature centrioles. The procentriole resembles a mature centriole in most respects except length: it is more annular than tubular. The daughter procentriole lies with its axis perpendicular to that of its parent. It presumably grows to full size during the late prophase, although the maturation stages have not been observed with the electron microscope. It is suggested that centrioles possess a constant polarization. The distal end forms the flagellum or other centriole products, while the proximal end represents the procentriole and is concerned with replication. The four centrioles of prophase (two parents and two daughters) are distributed by the two meiotic divisions to the four typical spermatids, in which they function as the basal bodies of the flagella. Atypical spermatocytes at first contain two normal centrioles. Each of these becomes surrounded by a cluster of procentrioles, which progressively elongate during the late prophase. After two aberrant meiotic divisions the centriole clusters give rise to the basal bodies of the multiflagellate sperm. These facts are discussed in the light of the theory, first proposed by Pollister, that the supernumerary centrioles in the atypical cells are derived from the centromeres of degenerating chromosomes.
FINE STRUCTURE OF THE SPERMATOZOON OF HYDROIDES HEXAGONUS (ANNELIDA), WITH SPECIAL REFERENCE TO THE ACROSOMAL REGION
Authors: Colwin Arthur L. , Colwin Laura Hunter
Published: May 2004

This paper describes in some detail the structure of the acrosomal region of the spermatozoon of Hydroides as a basis for subsequent papers which will deal with the structural changes which this region undergoes during fertilization. The material was osmium-fixed and mild centrifugation was used to aggregate the spermatozoa from collection to final embedding. The studies concern also the acrosomal regions of frozen-thawed sperm prepared by a method which previously had yielded extracts with egg membrane lytic activity. The plasma membrane closely envelops four readily recognizable regions of the spermatozoon: acrosomal, nuclear, mitochondrial, and flagellar. The acrosome consists of an acrosomal vesicle which is bounded by a single continuous membrane, and its periphery is distinguishable into inner, intermediate, and outer zones. The inner and intermediate zones form a pocket into which the narrowed apex of the nucleus intrudes. Granular material adjoins the inner surface of the acrosomal membrane, and this material is characteristically different for each zone. Centrally, the acrosomal vesicle is spanned by an acrosomal granule: its base is at the inner zone and its apex at the outer zone. The apex of the acrosomal granule flares out and touches the acrosomal membrane over a limited area. In this limited area the adjoining granular material of the outer zone is lacking. The acrosomal membrane of the inner zone is invaginated into about fifteen short tubules. The acrosomal membrane of the outer zone is closely surrounded by the plasma membrane. At the apex of the acrosomal region a small apical vesicle is sandwiched between the plasma membrane and the acrosomal membrane. Numerous frozen-thawed specimens and occasional specimens not so treated show acrosomal regions at the apex of which there is a well defined opening or orifice. Around the rim or lip of this orifice plasma and acrosomal membranes may even be fused into a continuum. The evidence indicates that the apical vesicle and the parts of the plasma and acrosomal membranes which surround it constitute a lid, and the rim of this lid constitutes a natural "fracture line" or rim of dehiscence. Should fracture occur, the lid would be removed and the acrosomal vesicle would be open to the exterior.
ELECTRON STAINS
Authors: Zobel C. Richard , Beer Michael
Published: May 2004

Chemical studies have been carried out on the interaction of DNA with uranyl salts. The effect of variations in pH, salt concentration, and structural integrity of the DNA on the stoichiometry of the salt-substrate complex have been investigated. At pH 3.5 DNA interacts with uranyl ions in low concentration yielding a substrate metal ion complex with a UO2++/P mole ratio of about ½ and having a large association constant. At low pH's (about 2.3) the mole ratio decreases to about ⅓. Destruction of the structural integrity of the DNA by heating in HCHO solutions leads to a similar drop in the amount of metal ion bound. Raising the pH above 3.5 leads to an apparent increase in binding as does increasing the concentration of the salt solution. This additional binding has a lower association constant. Under similar conditions DNA binds about seven times more uranyl ion than bovine serum albumin, indicating useful selectivity in staining for electron microscopy.