bluuebunny/crossref_metadata_2025 huggingface dataset:
Design of a GaN∕AlGaN intersubband Raman laser electrically tunable over the 3–5μm atmospheric transmission window
Authors: Sun Greg , Khurgin Jacob B. , Soref Richard A.
Published: February 2006

Design results aimed at achieving tunable high-temperature operation in the 3–5μm atmospheric transmission window are presented for the intersubband Raman lasers based on GaN∕AlGaN coupled quantum wells. The ultrafast longitudinal-optical-phonon (LO-phonon) scattering in GaN∕AlGaN quantum wells (QWs) can be used for the rapid depopulation of the lower laser state, while the large LO-phonon energies (∼90meV) allow for a design to minimize the thermal population of the lower laser state, and are therefore beneficial for obtaining high-temperature operation. The Raman gain is proportional to the difference between the virtual lifetime of the upper laser state and the effective lifetime of the lower laser state instead of the real lifetimes. The advantage is that these lifetimes can be tuned with the detuning of the pump photon energy from the subband energy separation. At a fixed pumping wavelength of 2.7μm, the tuning range of 3.6–5.2μm is predicted with a moderate Raman gain of at least 100∕cm as the electric field is varied. Furthermore, the output power of this laser is unlikely to saturate because of the intrinsically short intersubband lifetimes in the GaN-based QWs.
Ba
0.25
Sr
0.75
Ti
O
3
thin-film varactors on SrRuO3 bottom electrode
Authors: Khamchane K. , Vorobiev A. , Claeson T. , Gevorgian S.
Published: February 2006

Ba 0.25 Sr 0.75 Ti O 3 ∕ Sr Ru O 3 (BSTO/SRO) thin-film varactors were fabricated on (001)LaAlO3 substrates and characterized at rf and microwave frequencies of up to 10 GHz in the temperature range of 50–300 K. X-ray analysis reveals epitaxial growth of (001)-oriented BSTO films with extended out-of-plane lattice parameter b=3.925Å. The tensile out-of-plane strain (u33=0.3%) of BSTO films results in an out-of-plane component of the relative permittivity ε33=490. The renormalized Curie-Weiss constant and Curie temperature are C33=8.0×104K and T33=140K, respectively. An interfacial layer presumably forms at the Au∕Pt top electrode with a thickness-to-relative permittivity ratio of di∕εi=0.3–0.4nm and reduces the apparent relative permittivity to εa=250. The relative tunability of the varactor (at 10 V dc bias) increases from 40% (295 K) up to 80% (125 K) as the temperature decreases in the whole frequency range. The varactor loss tangent increases with increasing frequency and decreasing temperature (from tanδ=0.01 at 1 MHz and 295 K up to tanδ=1.7 at 10 GHz and 125 K, 0 V dc bias). The extrinsic loss of the BSTO film may be ascribed to charged defects associated with oxygen vacancies, at least in the temperature range of 150–300 K. This type of loss is mainly contributing to the total varactor loss balance in the frequency range of up to 500 MHz. At higher frequencies, the loss due to the SRO electrode series resistance starts to dominate. The commutation quality factor of the BSTO/SRO varactor is about 2000 at frequencies of up to 100 MHz and temperatures of less than 230 K, which is quite acceptable for practical applications.
Temperature and electric-field dependence of the mobility of a single-grain pentacene field-effect transistor
Authors: Minari Takeo , Nemoto Takashi , Isoda Seiji
Published: February 2006

A single-grain organic field-effect transistor (OFET) of pentacene with a 1μm channel length of top-contact electrodes is demonstrated in a wide range of temperatures from 300 down to 5.8K. No hysteresis behavior was observed in the transfer characteristics throughout the entire temperature range. The saturation mobility and on/off ratio are estimated at 1.11cm2∕Vs and 107 at 300K and 0.34cm2∕Vs and 105 at 5.8K, respectively. The nonmonotonic temperature dependence of the mobility indicates a bandlike transport at high temperatures. The electric-field dependence of the mobility in the single-grain OFET does not show a Poole-Frenkel-like behavior. This indicates that Poole-Frenkel-like behavior observed in conventional OFETs can be attributed to the disorder of molecules; single-grain OFET is free from such disorders.
Observation of the effect of grain orientation on chromium segregation in longitudinal magnetic media
Authors: Risner J. D. , Sinclair R. , Bentley J.
Published: February 2006

The nanoscale grain size of current hard disk media demands high-resolution methods for characterization. Therefore, high-resolution transmission electron microscopy (TEM), energy-filtered TEM (EFTEM) imaging, and nanoprobe energy-dispersive spectroscopy were chosen for the examination of Co84−x−yCr16PtxTay longitudinal hard disk media samples. Experiments were conducted to elucidate the relationship between nanoscale variations in grain-boundary composition and the atomic structure of the grain boundaries. Results show that Cr enriches the grain boundaries of the magnetic layer in all examined cases, but the addition of Ta greatly enhances this enrichment at some boundaries. Nanoprobe and EFTEM results show that enrichment varies according to the grain-boundary orientation of the hcp cobalt alloy crystals. Grains with tilt-boundary orientations near 0°, 30°, and 60°, found by measuring the angle between adjacent c-axis directions, show the least amount of segregation. Grains with tilt-boundary orientations near 15°, 45° and 75° show maximum amounts of Cr segregation. This trend exists in both CoCrTa and CoCrTaPt samples, and efforts to interpret the results within the context of hcp coincident site lattice theory are described.
Investigation of electronic transport in carbon nanotubes using Green’s-function method
Authors: Umegaki Toshihito , Ogawa Matsuto , Miyoshi Tanroku
Published: February 2006

We have investigated the fundamental transport characteristics in carbon nanotubes (CNTs) in order to realize a high-frequency device. In the present analysis, the electron and hole densities are excited at each lead and propagate as a wave from the left contact to the right contact in the CNTs. First, we applied Green’s-function method formulation to CNTs with arbitrary chirality. We then calculated the basic conductive characteristics in the CNTs. In the metallic and intrinsic CNTs, the assumption of a linearly varying potential distribution is valid because the electron and hole densities satisfy the charge neutrality condition, and their distributions become uniform. We evaluated the I-V characteristics of semiconductive and metallic CNTs. Based on the obtained results, we can control the differential conductance from a negative value to a value of several times the conductance quantum by means of chirality, Fermi level, and bias voltage. We evaluated the GV∕I-V characteristics of the zigzag CNT and found that when the group velocity of a mode with a real wave vector is comparable to that of another mode, GV∕I takes a maximum at V0, which corresponds to the transition between these modes.
Influence of lateral current spreading on the apparent barrier parameters of inhomogeneous Schottky diodes
Authors: Osvald J.
Published: February 2006

The influence of the series resistance of inhomogeneous Schottky diodes on the apparent barrier parameters in three different arrangements was studied. It is shown that when there is a total current spreading in the semiconductor substrate the ideality factor of the diode remains unity and the extracted series resistance is equal to the real value. On the other hand a lack of current spreading in the substrate results in the different voltage drops on the particular series resistances which causes different actual voltages on the particular diodes. The ideality factor nonequal to unity and the apparent series resistance different from the real value of the resistances are then the results of the barrier parameter extraction.
Microstructural origin of orientation ratio in magnetic recording media
Authors: Toney Michael F. , Marinero Ernesto E. , Hedstrom Jonathan A.
Published: February 2006

We report x-ray-diffraction measurements of the microstructural origin of circumferential magnetic anisotropy [or orientation ratio (OR), the ratio of the remanent magnetization along the circumferential and radial directions] in textured magnetic recording disks. We study a series of CoPtCrB magnetic media with CrX underlayers with varying OR and quantify the anisotropic strain in the CrX underlayer and the c-axis alignment in the hexagonal-close-packed media. Our data show that the c-axis alignment results from the anisotropic strain in the underlayer and suggest that the OR comes predominately from the media c-axis alignment.
Response to “Comment on ‘Modeling of the electron mobility in GaN materials’” [J. Appl. Phys. 99, 036106 (2006)]
Authors: Abdel-Motaleb Ibrahim M. , Korotkov R. Y.
Published: February 2006

We respond to the comments of Rode and Gaskill [J. Appl. Phys. 99, 036106 (2006)] on our paper “Modeling of the electron mobility in GaN materials” [J. Appl. Phys. 97, 093715 (2005)].
Comment on “Modeling of the electron mobility in GaN materials” [J. Appl. Phys. 97, 093715 (2005)]
Authors: Rode D. L. , Gaskill D. K.
Published: February 2006

We point out a potentially confusing characterization of an earlier work by Rode and Gaskill [Appl. Phys. Lett. 66, 1972 (1995)] which appeared in a recent paper by Abdel-Motaleb and Korotkov [J. Appl. Phys. 97, 093715 (2005)].
Correlation between outward diffusion of additives and oxidation of Cu(3.9at.%Ti) and Cu(2.3at.%Ta) thin films
Authors: Liu C. J. , Chen J. S.
Published: February 2006

Thin films of pure Cu and Cu alloys (with 3.9at.% Ti or 2.3at.% Ta) are deposited on SiO2∕Si substrates by magnetron sputtering. Upon annealing at 700°C in vacuum for 30min, Ti in the Cu(3.9at.%Ti) films will mostly diffuse to the free surface, but the majority of Ta in the Cu(2.3at.%Ta) film remains within the Cu layer. The outward diffusion of Ti or Ta strongly influences the oxidation of Cu in air. The degree of Cu oxidation was determined by glancing incident angle x-ray diffraction and the normalized sheet resistance. Oxidation test shows that the Cu(3.9at.%Ti) films exhibit a superior oxidation resistance when oxidized at 200°C in air, especially for the Cu(3.9at.%Ti) film which has been preannealed at 700°C in vacuum. But the Cu(2.3at.%Ta) film with the same preannealing treatment only slightly improves the oxidation resistance, in comparison with the pure Cu film. The correlation between outward diffusion of additives and oxidation of Cu in the Cu(3.9at.%Ti) and Cu(2.3at.%Ta) thin films is discussed.
Magnetic-field-induced strain in an antiferromagnetic γ-MnNi alloy
Authors: Peng W. Y. , Wang X. Y. , Zhang J. J. , Zhang J. H.
Published: February 2006

In the present study, the fcc→fct martensitic transformation and antiferromagnetic transition of the Mn82.2Ni17.8 alloy are studied by electric resistance measurement, dynamic mechanical analyzer, and transmission electron microscopy. The magnetic-field-induced strain associated with antiferromagnetic-order twin martensitic structure of the polycrystalline antiferromagnetic alloy is investigated. In addition, the threshold field of magnetic-field-induced strain of antiferromagnetic materials and the relation of antiferromagnetic domains and martensitic twins are discussed qualitatively.
A scaling law for the critical current of Nb3Sn stands based on strong-coupling theory of superconductivity
Authors: Oh Sangjun , Kim Keeman
Published: February 2006

We study the transition temperature Tc, the thermodynamic critical field Bc, and the upper critical field Bc2 of Nb3Sn with Eliashberg theory of strongly coupled superconductors using the Einstein spectrum α2(ω)F(ω)=λ⟨ω2⟩1∕2δ(ω−⟨ω2⟩1∕2). The strain dependences of λ(ε) and ⟨ω2⟩1∕2(ε) are introduced from the empirical strain dependence of Tc(ε) for three model cases. It is found that the empirical relation Tc(ε)∕Tc(0)=[Bc2(4.2K,ε)∕Bc2(4.2K,0)]1∕w (w≈3) is mainly due to the low-energy-phonon mode softening. We derive analytic expressions for the strain and temperature dependences of Bc(T,ε) and Bc2(T,ε) and the Ginzburg-Landau parameter κ(T,ε) from the numerical calculation results. The Summers refinement on the temperature dependence of κ(T) shows deviation from our calculation results. We propose a unified scaling law of flux pinning in Nb3Sn strands in the form of the Kramer model with the analytic expressions of Bc2(T,ε) and κ(T,ε) derived in this work. It is shown that the proposed scaling law gives a reasonable fit to the reported data with only eight fitting parameters.
Vibration analysis of embedded carbon nanotubes using wave propagation approach
Authors: Natsuki Toshiaki , Endo Morinobu , Tsuda Hiroshi
Published: February 2006

A vibration analysis of single- and double-walled carbon nanotubes as well as nanotubes embedded in an elastic matrix is presented using wave propagation approach. Approximate Flügge shell equations are proposed as the governing equations of vibration for the carbon nanotubes studied here. The double-walled nanotubes are assumed to be coupled together through the van der Waals force between the inner and outer nanotubes. For embedded carbon nanotubes, an elastic medium surrounding the nanotubes is described by a Winkler model. Effects of nanotube parameters and vibrational modes on the natural frequency are investigated and analyzed based on the proposed elastic continuum model.
Improved optical and electrical properties of low-temperature sputtered GaN by hydrogenation
Authors: Knox-Davies E. C. , Henley S. J. , Shannon J. M. , Silva S. R. P.
Published: February 2006

The room-temperature photoluminescence intensity and conductivity of GaN films grown by reactive rf sputtering were improved by the addition of hydrogen during growth. The differential resistivity decreased by two orders of magnitude when 2.4% H2 was added to the deposition gas. The improvement in the photoluminescence intensity occurred together with an increase in the level of oxygen contamination and an apparent increase in the structural disorder. At 0 and 20% H2, respectively, the refractive indices were 2.45 and 1.98, and the bandgaps were 3.06 and 3.64eV, with the change attributed to oxygenation.
Phase transitions in textured SrTiO3 thin films on epitaxial Pt electrodes
Authors: Keane Sean P. , Schmidt Steffen , Lu Jiwei , Romanov Alexei E. , Stemmer Susanne
Published: February 2006

Epitaxial Pt electrodes were used to control the orientation of 100–140-nm-thick SrTiO3 thin films deposited by radio-frequency magnetron sputtering. The influence of SrTiO3 thin-film microstructures on stress, dielectric properties, and phase transformations was studied. Epitaxial (111)-oriented SrTiO3 films were under compressive stress after growth, while predominantly (110)-oriented SrTiO3 films deposited under identical conditions changed from tensile to compressive stress with increasing film thickness. Measurements of the permittivity as a function of temperature showed that (111) films underwent a phase transformation at ∼150K, whereas predominantly (110)-oriented SrTiO3 films showed no deviation from linear Curie-Weiss behavior in the measured temperature range (100–300 K). Thermodynamic models that assumed a uniform compressive strain in the films did not predict a ferroelectric phase transformation for the (111)-oriented film in the measured temperature range. Possible explanations for the differences between the predictions of thermodynamic theory and the experiments are discussed.
High-performance thin-silicon-film transistors fabricated by double laser crystallization
Authors: Xu Li , Grigoropoulos Costas P. , King Tsu-Jae
Published: February 2006

Ultralarge-grained polycrystalline-silicon films have been formed from 50-nm-thick amorphous-silicon layers using double-laser crystallization (DLC). In situ images were captured to monitor the transient melting and solidification processes. Scanning electron microscope and plan-view transmission electron microscope analyses show that lateral grain dimensions up to 10μm can be achieved by this crystallization method. Prepatterning of the amorphous-silicon film prior to DLC provides a means for modifying the lateral temperature profile (hence grain structure) via edge cooling effects. Amorphous-silicon films as thin as 20 nm can be crystallized by DLC. Atomic force microscope images showed rms surface roughness less than 3 nm. High-performance n-channel thin-film transistors (TFTs) were fabricated in 50-nm-thick DLC films, with channel regions aligned to the large-grained regions, yielding electron field-effect mobilities as high as 124cm2∕Vs, threshold voltage as low as 0.2 V, and on-off current ratio as high as 108. The DLC poly-Si TFTs show substantially better performance than control devices fabricated via excimer laser crystallization.
Electroinductive waves in chains of complementary metamaterial elements
Authors: Beruete M. , Falcone F. , Freire M. J. , Marqués R. , Baena J. D.
Published: February 2006

Electronductive waves supported by chains of resonators drilled on a metallic plate are presented. Propagation of energy comes as a consequence of the electric coupling between these resonators. Therefore, these waves are termed as electroinductive waves. They can be interpreted as the dual counterpart of the so-called magnetoinductive waves, which are due to the mutual inductances along chains of resonators. In order to show their existence, some electromagnetic simulations and experiments have been carried out, using as resonators the complementary particle of the split ring resonator. The reported result opens the way to a high variety of applications in one- and two-dimensional devices, such as transducers, delay lines, bends, power dividers, couplers, antennas, lenses, etc.
Multichanneled filter based on a branchy defect in microstrip photonic crystal
Authors: Li Yunhui , Jiang Haitao , He Li , Li Hongqiang , Zhang Yewen , Chen Hong
Published: February 2006

A multichanneled filter based on a branchy defect in a microstrip photonic crystal is proposed. By introducing a branchy structure across the defect region, multiple defect modes will appear inside the photonic gap, leading to the multichanneled filtering phenomenon. In comparison with the conventional multichanneled filters, the proposed structure is more compact and tunable as far as the device volume and fabrication are concerned. The microwave experiment results are found in agreement with simulation results.
High-mobility bottom-contact n-channel organic transistors and their use in complementary ring oscillators
Authors: Yoo Byungwook , Jung Taeho , Basu Debarshi , Dodabalapur Ananth , Jones Brooks A. , Facchetti Antonio , Wasielewski Michael R. , Marks Tobin J.
Published: February 2006

The electrical characteristics of bottom-contact organic field-effect transistors fabricated with the air-stable n-type semiconductor N,N′-bis(n-octyl)-dicyanoperylene-3,4:9,10-bis(dicarboximide) (PDI-8CN2) are described. The mobility, threshold voltage, subthreshold swing, and Ion∕Ioff ratio(VDS=40V, VG=0∼40V) are 0.14cm2∕Vs, 1.6V, 2.0V/decade, and 1.2×103, respectively. The effect of electrode/dielectric surface treatment on these devices is also examined, with a combination of 1-octadecanethiol and hexamethyldisilazane. Organic complementary five-stage ring oscillators were fabricated using pentacene and PDI-8CN2, and operated at an oscillation frequency of 34kHz and a propagation delay per stage of 3μs.
Selective electroless plating to fabricate complex three-dimensional metallic micro/nanostructures
Authors: Formanek Florian , Takeyasu Nobuyuki , Tanaka Takuo , Chiyoda Kenta , Ishikawa Atsushi , Kawata Satoshi
Published: February 2006

We report on selective metal deposition over complex polymer structures formed by two-photon induced photopolymerization technique. Periodic three-dimensional micro/nanostructures are fabricated by means of a microlens array to produce multiple spots from a single-beam femtosecond laser. An electroless plating method is used to deposit a thin silver film onto the sample surface. The glass slide surface supporting the structures is chemically modified to avoid silver coating of the substrate. Our technique enables to produce complex metallic structures with arbitrary shapes under ambient conditions.
Blue light-emitting polymer with polyfluorene as the host and highly fluorescent 4-dimethylamino-1,8-naphthalimide as the dopant in the sidechain
Authors: Liu Jun , Min Changchun , Zhou Quanguo , Cheng Yanxiang , Wang Lixiang , Ma Dongge , Jing Xiabin , Wang Fosong
Published: February 2006

The dopant/host concept, which is an efficient approach to enhance the electroluminescence (EL) efficiency and stability for organic light-emitting diodes (OLEDs) devices, has been applied to design efficient and stable blue light-emitting polymers. By covalently attaching 0.2mol% highly fluorescent 4-dimethylamino-1,8-naphthalimide (DMAN) unit (photoluminescence quantum efficiency: ΦPL=0.84) to the pendant chain of polyfluorene, an efficient and colorfast blue light-emitting polymer with a dopant/host system and a molecular dispersion feature was developed. The single-layer device (indium tin oxide/PEDOT/polymer/Ca∕Al) exhibited the maximum luminance efficiency of 6.85cd∕A and maximum power efficiency of 5.38lm∕W with the CIE coordinates of (0.15, 0.19). Moreover, no undesired long-wavelength green emission was observed in the EL spectra when the device was thermal annealed in air at 180°C for 1h before cathode deposition. These significant improvements in both efficiency and color stability are due to the charge trapping and energy transfer from polyfluorene host to highly fluorescent DMAN dopant in the molecular level.
Breakfast: a review of associations with measures of dietary intake, physiology and biochemistry
Authors: Ruxton C. H. S. , Kirk T. R.
Published: February 2006

The present paper reviews the literature on breakfast to consider reported associations between breakfast and nutritional, physiological and biochemical variables. The contribution of breakfast to achieving nutrition targets for fat, carbohydrate and dietary fibre intakes is also examined as are the potential effects of fortified breakfast cereals on intakes of micronutrients and nutritional status. Breakfast consumption, particularly if the meal includes a breakfast cereal, is associated with lower intakes of fat and higher intakes of carbohydrate, dietary fibre and certain micronutrients. These findings may be relevant to population groups which could be at risk from low intakes of certain micronutrients, but further clarification of benefit is needed from studies of nutritional status. Associations between breakfast consumption and lower cholesterol levels have been reported, while lower body weights have been seen amongst breakfast eaters. It is concluded that breakfast consumption is a marker for an appropriate dietary pattern in terms of both macro- and micronutrients, particularly if breakfast cereals are included in the meal.
Giving Credit where it's Due: Promoting Financial Inclusion through Quality Credit Unions
Authors: Jones Paul A.
Published: February 2006

Early in 2005, HM Treasury established a Financial Inclusion Task Fund to support initiatives to tackle financial exclusion. It envisages that a substantial proportion of this funding will be allocated to third sector lenders such as credit unions operating in low-income areas. During the 1980s and early 1990s, public investment in credit unions was misdirected. This resulted in community credit unions remaining small and having only marginal impact within financially excluded communities. Since 1999, significant transformation has taken place in the credit union sector, which has resulted in credit unions developing as market-oriented and commercial social enterprises with a capacity to tackle financial exclusion both imaginatively and effectively at a borough wide, city-wide and sometimes county wide level.
Artifacts in 3D rotational angiography. an experimental study
Authors: Hagen G. , Lindgren P. G. , Jangland L. , Magnusson P. , Magnusson A.
Published: February 2006

Purpose: To investigate artifacts in three‐dimensional rotational angiography (3D‐RA) in an experimental model and to evaluate which parameters influence their distribution.

Material and Methods: 3D‐RA was carried out in a circular vessel phantom filled with contrast medium. Two different rotational angulations were used: 160° causing 64 images and 180° causing 90 or 120 images. The images were transferred to one workstation for reconstruction of axial slices and then to another workstation for 3D reconstructions. The 3D reconstructions were compared with standardized threshold settings.

Results: The artifacts occurred where the vessel had a longer path parallel to the rotation plane and became increasingly pronounced when the threshold level was raised. The artifacts decreased in size when rotation angle and number of projections were increased.

Conclusion: The quality of the 3D reconstructions from RA was degraded by beam‐hardening and sampling artifacts. The sampling artifacts were diminished by increasing both the rotation angle and the number of projections. The distortions in the 3D reconstructions caused by beam‐hardening remain to be resolved. The threshold values also had a considerable influence on the 3D reconstructions.
Magnetic resonance imaging of hyaline cartilage defects at 1.5T and 3.0T: comparison of medium T2‐weighted fast spin echo, T1‐weighted two‐dimensional and three‐dimensional gradient echo pulse sequences
Authors: Fischbach F. , Bruhn H. , Unterhauser F. , Ricke J. , Wieners G. , Felix R. , Weiler A. , Schröder R. J.
Published: February 2006

Purpose: To evaluate and compare the diagnostic accuracy of appropriate magnetic resonance (MR) sequences in the detection of cartilage lesions at 1.5T and 3.0T.

Material and Methods: Twelve chondral defects of varying depths, widths, and locations were created in the retropatellar hyaline cartilage in six sheep cadaver limbs. Axial images employing three fat‐suppressed imaging sequences – (1) a T2‐weighted fast spin‐echo (FSE) sequence, (2) a two‐dimensional (2D) and (3) three‐dimensional (3D) gradient‐echo (GE) sequence at 1.5T and 3.0T using an extremity quadrature coil – were evaluated by three experienced radiologists. Statistical analysis of the results consisted of receiver operating characteristics (ROC) and significant testing using the bivariate chi‐square test. In addition, signal‐to‐noise ratios (SNR) and contrast‐to‐noise ratios (CNR) were evaluated with significance testing using the Wilcoxon test.

Results: The 3D GE sequence compared favorably with other sequences at 3.0T and 1.5T (Az = 0.88 at 3.0T and Az = 0.85 at 1.5T) missing only one small grade 2 lesion. 2D GE imaging was inferior to 3D imaging at both field strengths ( P<0.05) in general. However, compared to 1.5T, lesion detectability was improved at the higher magnetic field of 3.0T (Az = 0.81 and 0.73 at 3.0T and 1.5T, respectively). FSE images showed significantly inferior sensitivity and less anatomical detail compared to the GE sequences at both field strengths (Az = 0.64 and 0.72 at 3.0T and 1.5T, respectively; P<0.05). However, compared to 1.5T, lesion detectability SNR and CNR values were superior in all sequences tested at 3.0T.

Conclusion: MRI at 3.0T improves SNR and CNR significantly in the most common sequences for cartilage MRI, resulting in an improvement in chondral lesion detection. GE imaging therefore allows resolution to be increased in an acceptable time manner for patient comfort, and the 3D GE fat‐suppressed sequence at 3.0T appears to be best suited for cartilage imaging in a clinical setting.
Diffusion tensor imaging of cerebral white matter in patients with myotonic dystrophy
Authors: Fukuda H. , Horiguchi J. , Ono C. , Ohshita T. , Takaba J. , Ito K.
Published: February 2006

Purpose: To determine whether myotonic dystrophy (MyD) patients have diffusion tensor abnormalities suggestive of microstructural changes in normal‐appearing white matter (NAWM).

Material and Methods: Conventional and diffusion tensor magnetic resonance images of the brain were obtained in 19 MyD patients and 19 age‐matched normal control subjects. Fractional anisotropy (FA) and mean diffusivity (MD) values were calculated in white matter lesions (WMLs) and NAWM in MyD patients and in the white matter of normal control subjects. Differences between WML and NAWM values and between MyD patient and control subject values were analyzed statistically.

Results: Significantly lower FA and higher MD values were found in all regions of interest in the NAWM of MyD patients than in the white matter of control subjects ( P<0.01), as well as significantly lower FA and higher MD values in WMLs than in NAWM of MyD patients ( P<0.05). There was no significant correlation of mean FA or MD values in NAWM with patient age, age at onset, or duration of illness ( P>0.1).

Conclusion: Diffusion tensor imaging analysis suggests the presence of diffuse microstructural changes in NAWM of MyD patients that may play an important role in the development of disability.
MRI combined with MR cholangiopancreatography versus helical CT in the evaluation of patients with suspected periampullary tumors: a prospective comparative study
Authors: Andersson M. , Kostic S. , Johansson M. , Lundell L. , Asztély M. , Hellström M.
Published: February 2006

Purpose: To establish the diagnostic accuracy of MRI including MR cholangiopancreatography (MRCP) compared with helical CT in the differentiation of malignant and benign lesions in the periampullary region.

Material and Methods: Fifty‐one patients (27 M, 24 F, mean age 66 years, range 39–86 years) with obstructive jaundice and sonographic evidence of intra‐ and extrahepatic bile duct dilatation ( n = 31) or suspicion of periampullary tumor, based on previously performed ultrasound and/or CT examination ( n = 20), were studied. MRI with MRCP and helical CT were reviewed blindly under standardized conditions. Lesion status (differentiation of malignant versus benign) was rated on a 5‐point diagnostic confidence scale. Reference standards for comparison were findings at surgery or laparoscopy and/or the clinical outcome. The predictive value of imaging findings was determined with multivariate logistic regression analysis.

Results: The areas under the receiver operating characteristic curve were 0.96 for MRI with MRCP and 0.81 for CT ( P<0.05). Multivariate analysis of eight imaging variables at MRI indicated that a stricture with malignant characteristics at MRCP was the best predictor of malignancy.

Conclusion: MRI with MRCP was significantly more accurate than CT in differentiating between malignant and benign lesions in patients with suspected periampullary tumors, mainly due to the information obtained on the MRCP images of the biliary and pancreatic duct anatomy.
Effect of dose on image quality in a detector‐based dual‐exposure, dual‐energy system for chest radiography
Authors: Freund T. , Fischbach F. , Teichgraeber U. , Lopez Haenninen E. , Eichstaedt H. , Felix R. , Ricke J.
Published: February 2006

Purpose: To assess the image quality of subtracted soft tissue and bone images of a CsI‐detector‐based dual‐energy system for chest radiography at varying dose levels.

Material and Methods: We evaluated a CsI‐detector‐based, dual‐exposure, dual‐energy prototype system; 126 patients were categorized into groups of small, medium, and large. Fixed values were applied for mAs and mA. The patients were randomized into two groups with intended higher and lower speed pairs of approximately 400/1000 (high and low energy shot) and 200/500, respectively. True speed equivalents were calculated retrospectively using the detector dose. Image quality was evaluated by two highly experienced radiologists in consensus applying a rating scale of 1 to 5 for quality indicators such as image noise, residual bone structures, motion artifacts, and others.

Results: Significantly decreased noise and a significant improvement for display of bone details in the bone image were noted with the higher dose, whereas a significant increase in motion artifacts reduced image quality at the higher dose.

Conclusion: Radiation dose did not significantly influence the perception of dual‐energy image quality. Dual‐energy subtraction, as described, has the potential to become a future routine application in chest radiography.
Neuroradiological findings in atypical teratoid/rhabdoid tumor of the central nervous system
Authors: Cheng Y.‐C. , Lirng J.‐F. , Chang F.‐C. , Guo W.‐Y. , Teng M. M.‐H. , Chang C.‐Y. , Wong T.‐T. , Ho D. M.‐T.
Published: February 2006

Purpose: To evaluate the computed tomography (CT) and magnetic resonance imaging (MRI) findings of atypical teratoid tumor/rhabdoid tumor (AT/RT) of the central nervous system (CNS).

Material and methods: Twenty cases of CNS AT/RT have been found over the past 23 years in our hospital; these involving 11 boys and 9 girls whose mean age at diagnosis was 5.5 years. Their clinical data, the CT, and MRI findings were reviewed retrospectively.

Results: AT/RT was located in the cerebellum in 15 cases. Four cases arose from the supratentorial region, while only one occurred primarily in the lumbar spinal cord. Almost all cases revealed heterogeneous intensity and heterogeneous enhancement. Peripheral cystic components were common. Survival time ranged from 2 months to 3 years, with a mean survival of 11.6 months.

Conclusion: Most cases of AT/RT are located in the cerebellum. The radiologic manifestations are non‐specific. The diagnosis mainly depends on the pathologic findings. However, AT/RT should still remain in the differential diagnosis of brain tumors in young children, especially those located in the cerebellar hemisphere and with eccentric cysts.
Central line‐associated venous late effects in children without prior history of thrombosis
Authors: Ruud Ellen , Holmstrøm Henrik , Hopp Einar , Wesenberg Finn
Published: February 2006

Background: The frequency of asymptomatic central line‐associated thromboses is high and well recognized among children with cancer, while the long‐term consequences are mainly unknown. Aim: In a cross‐sectional study, we evaluated clinical and radiological venous outcome in children with previous long‐standing intravascular catheters. Methods: The study enrolled 71 children previously treated for malignant or haematological diseases, 4–180 (median 37) mo after removal of their central lines. Inclusion criteria were a prior central line in a jugular vein for a minimum of 6 mo and no previous history of thrombosis. The children had clinical examination for post‐thrombotic syndrome (PTS) and Doppler ultrasonography of the central neck veins. Twelve children had additional venous magnetic resonance imaging (MRI). But no kind of venography was performed in the remaining. Results: We observed mild PTS with increased superficial collaterals in four children (6%), but no cases of more severe PTS. None complained of symptoms related to venous late effects. By ultrasonography, post‐thrombotic venous alterations were detected in 17 children (24%), and five of these had complete occlusion of the veins. The sensitivity for pathologically increased collaterals to identify occlusive thrombosis was 0.6, while the specificity was 0.98. Occlusive venous thromboembolism was associated with the total number of central venous lines (CVLs; p=0.002), previous severe CVL‐associated infections (p=0.001) and duration of central line in place (p=0.042).

Conclusion: In spite of no prior history of thrombosis, children with previous long‐term jugular lines frequently had local thrombotic sequelae, while clinical symptoms of PTS were rare.
Could Condoms Stop the AIDS Epidemic?
Authors: Moghadas Seyed M. , Gumel Abba B. , McLeod Robert G. , Gordon Richard
Published: February 2006

Although therapeutic treatment strategies appear promising for retarding the progression of HIV‐related diseases, prevention remains the most effective strategy against the HIV/AIDS epidemic. This paper focuses on the effect of condom use as a single‐strategy approach in HIV prevention in the absence of any treatment. There are two primary factors in the use of condoms to halt the HIV/AIDS epidemic: condom efficacy and compliance. Our study is focused on the effect of these factors in stopping the epidemic by constructing a new deterministic mathematical model. The current estimate of condom effectiveness against HIV transmission, based on the latest meta‐analysis, is 60–96%, with a mean of 87%. Since the parameter estimates are subject to different kinds of uncertainty, to achieve adequate quality assurance in predictions, uncertainty and sensitivity analyses are carried out using latin hypercube sampling (LHS) and partial rank correlation coefficients (PRCCs). Using stability and sensitivity analyses, based on a plausible range of parameter values, key parameters that govern the persistence or eradication of HIV are identified. This analysis shows that the product of efficacy and compliance, which we call ‘preventability’ (p), has a negative effect on the epidemic; as increasing p decreases the level of epidemicity. It is also shown that the threshold preventability (pc) increases with increasing average number of HIV‐infected partners of susceptible individuals, especially those in the AIDS stage. For populations where the average number of HIV‐infected partners is large, the associated preventability threshold is high and perhaps unattainable, suggesting that for such a population, HIV may not be controlled using condoms alone. On the other hand, for a population where the average number of HIV‐infected partners is low (within a reasonable range), it is shown that pc is about 75%, suggesting that the epidemic could be stopped using condoms. Thus, for such a population, public health measures that can bring preventability above the threshold and continuous quantitative monitoring to make sure it stays there, are what would be necessary. In other words, for populations with reasonable average numbers of HIV‐infected partners, given the will and effort, it is within our means to halt this epidemic using condoms.
A Haplotype Block Model for Fine Mapping of Quantitative Trait Loci Regulating HIV‐1 Pathogenesis
Authors: Zhu Yun , Hou Wei , Wu Rongling
Published: February 2006

The dynamic change of human immunodeficiency virus type‐1 (HIV‐1) particles that cause AIDS displays considerable variation from patients to patients. It is likely that such variation in HIV‐1 pathogenesis is correlated with the genetic architecture of hosts. Traditional genetic analysis of HIV‐1 infection is based on various biochemical approaches, but it has been little successful because HIV‐1 dynamics, as a complex trait, is under polygenic control and sensitive to environmental changes. Here, we present a novel model for integrating mathematical functions for HIV‐1 dynamics that have been well constructed into a multivariate mixture model for genetic mapping. This integrative mapping model on the foundation of linkage disequilibrium (LD)‐based haplotype block analysis provides unique power to precisely detect human quantitative trait loci (QTL) determining HIV‐1 dynamics and facilitates positional cloning of target QTL. The model allows for a number of hypothesis tests for the effects of the dynamic QTL on the virion clearance rate, the infected cell life‐span and the average viral generation time in vivo, all of which provide theoretical principles to guide the development of efficient gene therapy strategies.
Stochastic Cell
Authors: Kurakin Alexei
Published: February 2006

Accumulating experimental evidence of stochasticity, self‐organization and abrupt non‐linear transitions underlying the dynamics of cellular structure and function is increasingly more consistent with the concepts and models of phase transitions, critical phenomena and non‐linear thermodynamics rather than with the conventional clockwork description of the cell. The novel emerging image of the stochastic cell suggests that familiar and convenient classico‐mechanical interpretations may be limiting our ability to understand the behavior of biological systems and calls for active exploration of alternative interpretational frameworks.
IUBMB Life, 57: 59‐63, 2005
Primary Platelet Adhesion Receptors
Authors: Yip Jana , Shen Yang , Berndt Michael C. , Andrews Robert K.
Published: February 2006

Thrombotic diseases such as heart attack and stroke remain a major health concern in the Western world despite existing anti‐thrombotic drugs. Current studies are revealing structure‐function relationships of primary platelet adhesion receptors mediating adhesion, activation and aggregation, and the molecular mechanisms underlying platelet thrombus formation. Platelet adhesion is relevant not only to thrombotic disease, but there is increasing evidence of a specific role for platelets in vascular processes such as inflammation and atherogenesis. This review focuses on recent advances in understanding the molecular basis for platelet thrombus formation, in particular the receptors, glycoprotein (GP)Ib‐IX‐V and GPVI, that initiate platelet adhesion and activation at high shear stress.
IUBMB Life, 57: 103‐108, 2005
The Power and Potential of Doxorubicin‐DNA Adducts
Authors: Cutts Suzanne M. , Nudelman Abraham , Rephaeli Ada , Phillips Don R.
Published: February 2006

Doxorubicin (trade name Adriamycin) is a widely used anticancer agent which exhibits good activity against a wide range of tumors. Although the major mode of action appears to be normally as a topoisomerase II poison, it also exhibits a number of other cellular responses, one of which is the ability to form adducts with DNA. For adduct formation doxorubicin must react with cellular formaldehyde to form an activated Schiff base which is then able to form an aminal (N‐C‐N) linkage to the exocyclic amino group of guanine residues. The mono‐adducts form primarily at G of 5'‐GCN‐3' sequences where the chromophore of the drug is intercalated between the C and N base pair. The structure of the adducts has have been well defined by 2D NMR, mass spectrometry and X‐ray crystallography. The formation of these anthracycline adducts in cells grown in culture has been unequivocally demonstrated. The source of formaldehyde in cells can be endogenous, provided by coadministration of prodrugs that release formaldehyde or by prior complexation of anthracyclines with formaldehyde. Since the adducts appear to be more cytotoxic than doxorubicin alone, and also less susceptible to drug‐efflux forms of resistance, they offer new approaches to improving the anticancer activity of the anthracyclines.
IUBMB Life, 57: 73‐81, 2005
Inactivation of the PRDM1/BLIMP1 gene in diffuse large B cell lymphoma
Authors: Pasqualucci Laura , Compagno Mara , Houldsworth Jane , Monti Stefano , Grunn Adina , Nandula Subhadra V. , Aster Jon C. , Murty Vundavally V. , Shipp Margaret A. , Dalla-Favera Riccardo
Published: February 2006

PR domain containing 1 with zinc finger domain (PRDM1)/B lymphocyte–induced maturation protein 1 (BLIMP1) is a transcriptional repressor expressed in a subset of germinal center (GC) B cells and in all plasma cells, and required for terminal B cell differentiation. The BLIMP1 locus lies on chromosome 6q21-q22.1, a region frequently deleted in B cell lymphomas, suggesting that it may harbor a tumor suppressor gene. We report here that the BLIMP1 gene is inactivated by structural alterations in 24% (8 out of 34) activated B cell–like diffuse large cell lymphoma (ABC-DLBCL), but not in GC B cell–like (n = 0/37) or unclassified (n = 0/21) DLBCL. BLIMP1 alterations included gene truncations, nonsense mutations, frameshift deletions, and splice site mutations that generate aberrant transcripts encoding truncated BLIMP1 proteins. In all cases studied, both BLIMP1 alleles were inactivated by deletions or mutations. Furthermore, most non–GC type DLBCL cases (n = 20/26, 77%) lack BLIMP1 protein expression, despite the presence of BLIMP1 mRNA. These results indicate that a sizable fraction of ABC-DLBCL carry an inactive BLIMP1 gene, and suggest that the same gene is inactivated by epigenetic mechanisms in an additional large number of cases. These findings point to a role for BLIMP1 as a tumor suppressor gene, whose inactivation may contribute to lymphomagenesis by blocking post–GC differentiation of B cells toward plasma cells.
Sputum Induction Problems Identified Through Genetic Fingerprinting
Authors: Nivin Beth , O'Flaherty Tholief , Leibert Eric , Zhao Ben Yang , Driscoll Jeffrey
Published: February 2006

Objective:

To identify the contamination source of a cluster of eight positiveMycobacterium tuberculosisisolates from one laboratory session.

Methods:

Spoligotyping was performed onM. tuberculosisisolates processed during one laboratory session. Laboratory and sputum induction protocols and records were reviewed. Sputum induction staff were interviewed. An environmental assessment of the sputum induction booth was performed.

Results:

Spoligotyping identified a unique strain of susceptibleM. tuberculosisfrom five induced sputa collected at Clinic A on the same day. Three specimens processed concurrently from other clinics had spoligotypes different from each other and from the cluster strain. A laboratory investigation revealed no procedural lapses. Sputum induction records from Clinic A indicated that patient 1 in the sputum induction booth had prior culture-confirmed tuberculosis. Patient 2 had a history of a drug-resistant strain. Patient 3 had completed tuberculosis treatment, with positive cultures 7 months earlier. Patients 4 and 5 were new to the clinic and had no subsequent positiveM. tuberculosisspecimens. The sputum induction booth was working within normal parameters. Sputum induction that day was overseen by a new employee with limited training and no supervision. A review of the sputum induction protocol identified ambiguity regarding care of the ultrasonic nebulizer between patients, which may have led to reuse of the discarded nebulizer solution from patient 1.

Conclusions:

A break in the sputum induction protocol may have contributed to contamination of patient specimens. Sputum induction is complicated, mandating adequate staff training and supervision and patient preparation. Spoligotyping identified a potential source ofM. tuberculosiscontamination.(Infect Control Hosp Epidemiol 2002;23:580-583).
Delays in the Application of Outbreak Control Prophylaxis for Influenza a in a Nursing Home
Authors: Drinka Paul J. , Krause Peggy , Nest Lori , Gravenstein Stefan , Goodman Brian , Shult Peter
Published: February 2006

Objective:

To identify delayed prophylaxis from a preexisting database and strategies to improve performance.

Setting:

A skilled nursing facility with 14 floors (4 buildings). The “outbreak unit” was a 50- to 60-bed floor.

Methods:

We performed surveillance during six seasons using one protocol. Prophylaxis was started when influenza was cultured in the building and 10% of residents on the floor had a new respiratory illness within 7 days. We defined delayed prophylaxis as four or more residents on a floor with positive cultures whose specimens had been collected within 5 days before the application of prophylaxis.

Results:

We identified 14 examples of delayed prophylaxis. In three, delayed prophylaxis was related to the 3.9-day delay between culture collection and culture report. There was a high degree of commonality among building attack rates within a season. During six seasons, the first case in the last building occurred 27 to 64 days after the first case in the facility. The two seasons with the greatest activity (68 and 154 cases, respectively) began with explosive, multi-floor outbreaks in a single building. The match between the circulating strain and the vaccine was good, except in 1997-1998 when there were seven examples of delayed prophylaxis.

Conclusions:

Influenza may involve buildings sequentially with a commonality of building attack rates. Explosive, multi-floor outbreaks early in the season could lead to a lower threshold for prophylaxis within a larger area when initial cases are encountered later in the season. This strategy could have prevented five examples of delayed prophylaxis. Rapid testing of multiple specimens while waiting for culture confirmation could have prevented three examples of delayed prophylaxis. (Infect Control Hosp Epidemiol 2002;23:600-603).