bluuebunny/crossref_metadata_2025 huggingface dataset:
Intraparticle Mass Transfer in High‐Speed Chromatography of Proteins
Authors: Farnan Dell , Frey Douglas D. , Horváth Csaba
Published: July 2002

The effect of intraparticle mass‐transfer resistances on the peak shape at high flow velocities in the range currently used in high‐speed protein chromatography was investigated both theoretically and experimentally. The asymmetry of the protein bands under these conditions was quantified by the difference between the first moment and the retention volume of the peak apex, this being much easier to determine than the peak skewness. A general method is introduced for the evaluation of the mass‐transfer characteristics of a given chromatographic sorbent from the variation in peak asymmetry with reduced velocity. The method is shown to be most useful when the number of theoretical plates is between 3 and 300, which is the regime where peak asymmetry is prevalent. Measurements by isocratic elution under nonretained conditions were made on three chromatographic sorbents, each representing a general class of stationary phase configuration, i.e., gigaporous, mesoporous, and gel‐filled gigaporous particles. Mass‐transfer parameters were evaluated using the new method based upon the variation of the peak asymmetry with the fluid velocity. For the purpose of comparison, column mass transfer parameters were also evaluated from the variation in the reduced plate height with reduced velocity, a method most useful when the peak asymmetry is small and remains constant in the velocity range investigated. It is shown that the two methods are complementary and yield, within experimental error, the same intraparticle diffusion parameters. It was demonstrated using these methods that the diffusional behavior and the first moments of unretained eluites for the gel‐filled gigaporous column packing correspond to a sorbent particle where eluites diffuse through liquid‐filled pores containing a uniform distribution of solid cylinders, with the cylinders representing the polymer chains in the gel material. Similarly, the methods were used to verify that, at high flow rates, intraparticle convection can contribute substantially to the rate of intraparticle mass transfer in gigaporous column packings.
The threshold concept in food safety and its applicability to food allergy
Authors: O'B Hourihane Jonathan
Published: July 2002

Down the years there have been many clinical reports of exquisite sensitivity to low doses of food allergens. There are many factors that may contribute to a variation of threshold in an individual exposed to an allergen during the course of his or her daily life. Some of these factors are intrinsic and unavoidable. Other factors may be predictable but not easily controllable, such as asthma, exposure to allergens during the pollen season and predicting situations that may be risky. Other factors may be out of the control of the individual. The most important one of these is the adequate training and awareness of manufacturers and caterers who aim to provide safe and nutritious meals to their allergic and non‐allergic customers alike. Clinical histories of reactions in the community and the use of labial exposure during food challenge show that most non‐ingestion exposures to peanut usually result in easily treated minor reactions. Formal, oral food challenges have shown that low dose reactivity is relatively common but studies have not yet had the power to investigate whether peanut allergy is more commonly associated with very low dose reactivity than other foods. This means that industry must not concentrate only on peanut and tree nuts when looking at issues of contamination just because they are associated with the majority of severe reactions. There are more milk and egg allergic children in the general population and they deserve the same protection from allergen exposure as sufferers of peanut or tree nut allergies.
Characteristics of maternal directiveness and responsiveness with young children with visual impairments
Authors: Hughes M. , Dote‐Kwan J. , Dolendo J.
Published: July 2002

The purpose of this study was to investigate the relation between maternal responsive and directive behaviours and the development of young children with visual impairments. The participants were 17 mother–child dyads, and the children’s ages ranged from 20 to 36 months of age. The amount, quality, and appropriateness of four maternal behaviours were rated during a free play session between mother and child and compared with a developmental outcome measure designed for young children with visual impairments. In general, the results showed that the quality of maternal control and appropriateness of directiveness were positively related to children’s language development; whereas, the amount of these same behaviours was negatively related to language development. The findings also indicated that both the quality and amount of maternal goal‐setting behaviours, and the quality of responsiveness were positively related to children’s language skills, exploration of the environment and sensorimotor development. The findings are discussed in terms of maternal influence on child development.
Comparison of six months therapy with octreotide versus lanreotide in acromegalic patients: a retrospective study
Authors: Razzore P. , Colao A. , Baldelli R. , Gaia D. , Marzullo P. , Ferretti E. , Ferone D. , Jaffrain‐Rea M.L. , Tamburrano G. , Lombardi G. , Camanni F. , Ciccarelli E.
Published: July 2002

OBJECTIVE

We analysed the effects of 6‐months' treatment with octreotide s.c. and lanreotide‐SR on circulating GH and IGF‐I levels in acromegaly.

DESIGN

Open retrospective study.

PATIENTS

Thirty‐eight patients with active acromegaly (plasma IGF‐I levels greater than 2 standard deviations for age‐matched controls and increased serum GH levels not suppressible by oral glucose load) were studied. All patients received s.c. octreotide at a dose of 150‐600 μg/day for six months as first therapy and subsequently, lanreotide i.m., 30‐60 mg either at 14 or 10 day intervals, for 6 months. A 3 months' washout was applied before starting lanreotide treatment.

MEASUREMENTS

Mean serum GH levels (from three samples), IGF‐I, and clinical examination were performed before and 30, 60, 90 and 180 days after octreotide and lanreotide treatments. Safety tests, HbA1c and, thyroid function were evaluated every three months.

RESULTS

Circulating GH and IGF‐I levels were significantly reduced (P < 0.001) after one, three and six months of both octreotide and lanreotide treatment. The absolute values were lower and the percent decrease in serum GH levels obtained after octreotide treatment was significantly greater, at all scheduled assessments, than after lanreotide (P < 0.01). Serum IGF‐I levels during octreotide were significantly lower only after the first month of therapy (P < 0.01).

CONCLUSIONS

Our study shows that octreotide s.c. is able to induce an earlier reduction in IGF‐I levels and a more marked reduction in GH levels than lanreotide. However, after six months of therapy the number of patients with safe GH levels and normal IGF‐I age‐matched levels, was similar with both drugs. Therefore we suggest that octreotide treatment be preferentially used in the short‐term presurgical treatment, while lanreotide can be used in chronic therapy when better compliance is necessary.
White clover growth patterns during the grazing season in a rotationally grazed dairy pasture in New York
Authors: Karsten H. D. , Fick G. W.
Published: July 2002

White clover (Trifolium repens L.) is an important stoloniferous pasture legume in the Great Lakes region of the United States, but it often has limited persistence. Researchers in New Zealand and Wales have found that in spring, compared with other seasons, white clover plants have reduced branching complexity and have the fewest buds that produce leaves. They therefore suggested that in spring the plants are most vulnerable to grazing and climatic stress.

Because of severe winter and cool, wet spring weather in New York State, it was hypothesized that white clover plants would also be of low branching complexity, smaller and have low axillary bud activity in spring compared with later in the grazing season. To test this, growth of white clover was monitored in an orchard grass (Dactylis glomerata L.)/white clover pasture in New York that was rotationally grazed with dairy cows during the 1993 and 1994 grazing seasons.

Three sets of plants were sampled. The first set consisted of forty random plants sampled before each grazing event. Stolon branching order, number of each stolon branching type and area the plant occupied were determined. Approximately each month before one grazing event, a separate set of 32 random plants was measured in the field to determine the area they occupied; these plants were then removed to the laboratory for the measurement of stolon order, number of each stolon type, stolon lengths, total number of growing points, number of taproots and adventitious roots, root position and above‐ground dry matter. Once a month, 12 additional plants were removed to measure axillary bud activity at each node.

Leaf development from nodes tended to increase from spring to summer. However, the stolon branching order of white clover plants was not simpler in spring compared with summer or autumn. In 1994 during and after a dry and hot period, white clover plants were smaller, of lower stolon branching order and had fewer roots. Climate and associated soil organism activity appear to explain the different white clover growth patterns observed in New York and New Zealand. Severe winters in New York limit earthworm activity and stolon burial, which is important in contributing to stolon/plant breakdown in New Zealand. During the years of this study in New York, a hot and dry period had the most negative effect on the growth pattern of white clover.
Chinese consumer types
Authors: Li Haifeng , Xiao Jing J.
Published: July 2002

Abstract: Based on data from a survey carried out in Beijing and a correspondence analysis, Chinese consumers are categorized into four types. Among them, 50.8% are the ‘pragmatic’ type, who seek practical aspects of consumer goods and ignore commercial information, 33.9% are the ‘commercialized’ type, pursuing commercial information and brand name products, 11.7% are the ‘sociable’ type, getting information mainly from friends, and only 3.6% are the ‘conservative’ type, resenting commercial information and disliking social changes. According to the trend of demographic and economic factors, more Chinese will become the ‘commercialized’ type in the future.
An audit of laxative use and fibre/fluid intakes in a care of the elderly rehabilitation ward
Authors: Grant E.
Published: July 2002

Background: Constipation is a common problem in elderly patients, resulting in considerable discomfort and expenditure on prescribed laxatives.

Aims and objectives: This study aimed to audit the use of laxatives on a ward for the rehabilitation of elderly people; to assess the fibre and fluid provided to patients on the basis of hospital menus and to assess the individual, daily intakes of fluid and fibre of three patients.

Methods: Pharmacy records were used to audit laxative use on the ward over a 3‐month period. Provision of fluid and fibre were assessed by analysis of the regular and soft menus for 3 days, using food composition tables. A weighed intake assessment of three patients for one day was undertaken.

Results: Ispaghula husk (Fybogel, Regulan) were the most commonly used laxatives. Although the regular menu appeared to provide adequate amounts of fluid and fibre, results for the soft menu were less satisfactory. All three patients had intakes well below the recommended level of dietary fibre.

Conclusion: Despite the limitations of this small study, the findings suggest that improvements in catering and food service could be implemented to increase the intake of dietary fibre by patients in this ward. These should be implemented and the use of laxatives re‐audited.
Diverse T‐Cell Receptor CDR3 Length Patterns in Human CD4+ and CD8+ T Lymphocytes from Newborns and Adults
Authors: Halapi E. , JEDDI‐TEHRANI M. , BLÜCHER Å. , ANDERSSON R. , ROSSI P. , WIGZELL H. , GRUNEWALD J.
Published: July 2002

T cells are essential in the initiation and maintenance of immune responses. Specific interaction between T cells and a presumptive antigen occurs through recognition of an MHC—peptide complex by the T‐cell receptor (TCR). The complementarity‐determining region (CDR) 3 of the TCR has direct contact with the peptide. Here we describe CDR3 length variability of six different TCRBV gene families of CD4+ and CD8+ umbilical cord (UC) and peripheral blood (PB) T cells. Amplified products spanning the TCR CDR3 regions from CD4+ PB, CD4+ UC and CD8+ UC blood T cells typically displayed Gaussian‐like distributions. In contrast, profound and frequent perturbations were recorded in CD8+ PB lymphocytes, with a non‐Gaussian pattern in more than half of the samples studied. A substantial portion of the perturbed CD8+ subsets were clonal or oligoclonal, as determined by CDR3‐length restriction, TCRBJ gene usage and nucleotide sequencing. This implies that the conditions for shaping and maintenance of the peripheral TCR repertoire are profoundly different for CD8+ and CD4+ T cells.
Modulation of the Immune Response by Progesterone‐Induced Lymphocyte Factors
Authors: BOREL I. M. , FREIRE S. M. , RIVERA E. , CANELLADA A. , BINAGHI R. A. , MARGNI R. A.
Published: July 2002

Rat spleen and peripheral blood lymphocytes express progesterone receptors whose concentration is increased greatly during the early phase of pregnancy. After stimulation of progesterone the expression of receptors was augmented 2–3 times. When cells were cultured in the presence of progesterone they released a soluble factor that inhibited cellular immunoreactions (MLR, CRC) and cellular proliferation as measured by thymidine incorporation by spleen‐cell culture. This factor also inhibited the synthesis of anti‐DNP antibodies by a mouse hybridoma and diminished the proportion of cells in phase S. However, the percentage of asymmetric molecules produced by the hybridoma remained unaltered. These results support the hypothesis that soluble factors released by rat lymphocytes modulate the immune response of the mother and participate in the mechanism that protects the fetus against antipaternal antibodies.
Synthesis, biology, NMR and conformation studies of the topographically constrained δ‐opioid selective peptide analogs of [β‐iPrPhe3]deltorphin I
Authors: Liao S. , Shenderovich M. , Zhang Z. , Hruby V.J. , Kövér K.E. , Hosohata K. , Davis P. , Porreca F. , Yamamura H.I.
Published: July 2002

Abstract: Replacement of Phe3 in the endogenous δ‐opioid selective peptide deltorphin I with four optically pure stereoisomers of the topographically constrained, highly hydrophobic novel amino acid β‐isopropylphenylalanine (β‐iPrPhe) produced four pharmacologically different deltorphin I peptidomimetics. Radiolabeled ligand‐binding assays and in vitro biological evaluation indicate that the stereoconfiguration of the iPrPhe residue plays a crucial role in determining the binding affinity, bioactivity and selectivity of [β‐iPrPhe3]deltorphin I analogs: a (2S,3R) configuration of the iPrPhe3 residue in [β‐iPrPhe3]deltorphin I provided the most desirable biological properties with binding affinity (IC50 = 2 nm), bioassay potency (IC50 = 1.23 nm in MVD assay) and exceptional selectivity for the δ‐opioid receptor over the µ‐opioid receptor (30 000). Further conformational studies based on two‐dimensional NMR and computer‐assisted molecular modeling suggested a model for the possible bioactive conformation in which the Tyr1 and (2S,3R)‐β‐iPrPhe3 residues adopt trans side‐chain conformations, and the linear peptide backbone favors a distorted β‐turn conformation.
Comparison of two Doppler ultrasound criteria for grading cervical internal carotid artery stenosis
Authors: Wong James Kl , Gibson Robert N , Mitchell Peter J
Published: July 2002

In a review of 49 carotid arteries that had been assessed by ultrasound and angiography, two Doppler criteria were compared for accuracy in grading internal carotid artery (ICA) stenosis. The Seattle criteria for Doppler spectral analysis and the internal‐to‐common carotid artery peak systolic velocity ratio were of similar accuracy. When used in combination, there was an increase in sensitivity compared with the use of a single criterion. The velocity ratio had a higher sensitivity for detection of high‐grade stenosis, but it tended to overestimate the grade of stenosis more than the Seattle criteria. To increase the sensitivity for detection of severe stenosis, the criteria should be used together and the higher grade of stenosis should be taken if there is a mismatch in assessment.
Lymphangiomyomatosis: Radiological and measured lung function deterioration after contrast‐enhanced computed tomography
Authors: Teo MSK , Tan LKA , Lim TK
Published: July 2002

Pulmonary lymphangiomyomatosis (LAM) is a rare disease of unknown aetiology which occurs exclusively in women, usually of reproductive age. The findings on CT and high‐resolution CT (HRCT) are well described and characteristic, and in a young woman they are virtually pathognomonic. A case of symptomatic, radiological and measured lung function deterioration following contrast‐enhanced CT in a patient with LAM are reported here. These observations, to the authors’ knowledge, have never been reported before. The authors attempt to explain these observations based on the known pathology of LAM.
Kuhse on caring
Authors: Van Hooft Stan
Published: July 2002

After a brief description of Helga Kuhse’s arguments on the place of caring in moral decision‐making in her recent book, Caring: Nurses, Women and Ethics, the author suggests that Kuhse is committed to reasons externalism and to a moderate form of motivational externalism. This compartmentalizes the psychology of moral agency and fails to see caring as the holistic stance toward patients which some nursing theorists have been espousing. The author then goes on to sketch such a holistic conception and to overcome difficulties relating to objectivity, the place of practical reason, and to weakness of will, which the new conception raises.
Surgery as salvage therapy in chemotherapy‐resistant nonseminomatous germ cell tumours
Authors: Ravi  , Ong  , Oliver  , Badenoch  , Fowler  , Hendry
Published: July 2002

Objective

 To review our experience of surgical staging for residual masses after chemotherapy in patients with nonseminomatous germ cell tumour (NSGCT) and positive tumour markers.

Patients and methods

 Of 107 patients with metastatic NSGCTs treated surgically after chemotherapy from 1978 to 1995, 30 (median age 30.5 years, range 20–52) had positive tumour markers. These patients were reviewed and the outcome compared with 77 patients who had normal tumour marker values.

Results

 Of the 77 patients with negative markers undergoing surgical/pathological staging, 71 (92%) became continuously disease‐free, including 37 of 50 (74%) with viable NSGCT in excised specimens. Seventeen of 30 (57%) with raised marker levels undergoing similar surgery for chemotherapy‐resistant tumour became disease‐free, including 11 of 22 with viable NSGCT in the excised specimens.

Conclusion

 Although the outcome after surgery is better in patients with negative tumour markers, it is clear that surgery is curative for patients with localized chemotherapy‐resistant masses. There is a need for continued debate on the timing of salvage surgery and subsequent chemotherapy.
Insulin secretion and action in different stages of glucose tolerance in Asian Indians
Authors: Snehalatha C. , Satyavani K. , Sivasankari S. , Vijay V. , Ramachandran A.
Published: July 2002

Aims

To evaluate the sequence of changes in insulin secretion and action in different stages of glucose tolerance and the effect of obesity on insulin profile in South Indian adults. Blood samples from 260 consecutive cases with no known history of diabetes were collected. Plasma insulin levels were measured during a 75‐g oral glucose tolerance test. Insulin resistance (IR) was calculated, using the homeostasis model assessment (HOMA). An index of insulin secretion was derived as the ratio of incremental insulin at 30 min divided by 30 minute plasma glucose (Δ I/G)

Results

Normoglycaemia was present in 164, impaired glucose tolerance (IGT) in 60 and diabetes in 36 subjects. Fasting and 2 h insulin secretion showed bell shaped curves with increasing plasma glucose. The peak values corresponded to the cut‐off values used for the diagnosis of clinical diabetes. IR was higher in obese than in nonobese, nondiabetic subjects but the effect of obesity on IR was not found in subjects with diabetes. IGT was associated with higher IR, but not with evidence of a β‐cell defect.

Conclusions

Evaluation of insulin resistance and β‐cell function in different stages of glucose tolerance indicate that insulin resistance is manifested in the early stage of glucose intolerance in South Indians, i.e. IGT. A β‐cell defect was mostly found in people with diabetes. The β‐cell defect is more common in diabetes among the nonobese.
Optometrist screening for diabetic retinopathy: evidence and environment
Authors: Mason James , Drummond Michael , Woodward Geoff
Published: July 2002

A recent English government‐funded study has suggested that optometrists are not best suited to screening for diabetic retinopathy. This is surprising given the level of training of optometrists and their aptitude in detecting other conditions such as glaucoma and cataract.

The need to screen for diabetic retinopathy is discussed. The major unresolved issue concerns the choice of screening modality, i.e. who should perform screening, when and how. A literature search is reported. Given the available evidence, to make conclusions about the relative performance of optometrists with other screeners would be inappropriate.

Unresolved controversies could be addressed by new prospective studies of optometrists, and others, in screening. A pragmatic design, mirroring the current environment of care, may be important. In particular, the manner in which diabetics currently present to the health service would make screening by one modality of limited use. If thoughtfully applied, shared care concepts may achieve a broader coverage of patients with diabetics mellitus. Smaller trials investigating sub‐issues, and surveys of patients and potential screeners may produce a valuable backdrop in designing appropriate studies.

Issues for the development of screening schemes are considered, including the role of training, the development of protocols for care and sharing data, reimbursement and audit.
Why Daily Hemodialysis Is Better: Decreased Unphysiology
Authors: Kjellstrand Carl M , Ing Todd S
Published: July 2002

We are entering a whole new field for studies of how to quantitate and optimize the effects of hemodialysis. Over 30 years of experience in treating more than 200 patients with daily hemodialysis has shown that this standard of care brings about marked improvement in hematology, blood pressure regulation, nutrition, tolerance of dialysis, interdialysis symptoms, and quality of life. These improvements occur within weeks or months after daily hemodialysis is begun, even if the dose of dialysis, “Kt/V”, is decreased; thus, these improvements are not accounted for by changes in Kt/V. We propose that this is due to decreased “unphysiology”: decreased oscillations in osmolality and body fluid volumes and smaller deviations from normal electrolyte and acid‐base balance, both before and after a hemodialysis session. How to summarize these changes is presently unknown. Previous attempts to quantitate them include sums of osmolality changes, weight changes during dialysis and potassium changes, and more recently, the “time averaged deviation” (TAD) concept. The task of determining the factors contributing to these changes probably requires much more sophisticated quantitation. We suggest one “direct” measurement formula and one “indirect” formula. We also suggest that the Kt/V concept be abandoned and replaced with direct measurements of dialysis creatinine clearance, combining that achieved by intermittent or continuous dialysis methods with remaining renal function.
Pain in ambulatory HIV‐infected patients with and without intravenous drug use
Authors: Martin Claes , Pehrsson PehrOlov , Österberg Anders , Sönnerborg Anders , Hansson Per
Published: July 2002

The prevalence of pain in 211 HIV‐infected patients with and without intravenous drug use was assessed and the prognostic information inherent in pain reporting was evaluated, using a questionnaire on pain and HIV‐related symptoms combined with data on disease classification, route of HIV transmission, CD4+ lymphocyte counts in blood (CD4) and mortality rates at 15 months after completing the questionnaire. The pain prevalence was significantly higher among intravenous drug users (IDUs) compared with non‐IDUs [76/89 (85%) vs 87/122 (71%);p<0.05], especially among the patients classified as asymptomatic [43/53 (81%) vs 35/59 (59%);p = 0.01]. No significant difference was found among AIDS patients. In non‐IDUs, a strong correlation was found between HIV disease stages according to the Centers for Disease Control classification (CDC) and pain prevalence (CDC A: 59%vs B: 74%vs C: 96%, p<0.001), and between the number of concurrent pain sites and both the CD4 levels (no pains: CD4 0.26 × 109/l vs 1–2 pain sites: CD4 0.22 vs>2 pain sites: CD4 0.09;r = 0.35, p<0.001), and the mortality rate [no pains: 2/35 (6%) vs 1–2 pain sites: 8/45 (18%) vs> 2 pain sites: 12/42 (29%), p<0.01]. In IDUs, no such correlations were found. Our data demonstrates differences in the development, prevalence and prognostic value of pain among HIV‐infected patients, with and without intravenous drug use, clearly indicating the need to differentiate risk groups in pain related studies.
NMR Study of Chloroplast Water in Acer platanoides: Water Exchange at Membrane‐Bound Sites and Across the Chloroplast Envelope Membrane
Authors: McCain D. C.
Published: July 2002

Abstract: Nuclear magnetic resonance (NMR) spin relaxation techniques were used to measure the rate of water exchange across the chloroplast envelope membrane and to detect exchange of water‐hydrogens between the bound and fluid states in Acer platanoides shade leaves. Results indicate that individual water molecules resided within a chloroplast for 320 ± 65 ms, on average, before exchanging through the envelope, and that exchangable bound hydrogens are at least six times more abundant in the chloroplast than in the nonchloroplast compartments.
Polymorphism and crystal-crystal transformations of the highly optically nonlinear organic compound α-[(4′-methoxyphenyl)methylene]-4-nitro-benzeneacetonitrile
Authors: Oliver S. N. , Pantelis P. , Dunn P. L.
Published: July 2002

Crystals of α-[(4′-methoxyphenyl)methylene]-4-nitro-benzeneacetonitrile exhibit powder second-harmonic generation (SHG) efficiencies under 1.06 μm irradiation several times that of 2-methyl-4-nitroaniline. We have identified three distinct, solution-grown polymorphs which show marked variation in SHG efficiency. Controlled transformation between these polymorphs can be made either solvent assisted or thermally. One polymorph shows a 25-fold increase in SHG efficiency when the irradiation wavelength is changed to 1.32 μm while the others show a small or no increase.
Phase-matched second-harmonic generation in a polymer waveguide
Authors: Khanarian G. , Norwood R. A. , Haas D. , Feuer B. , Karim D.
Published: July 2002

Quasi-phase-matched second-harmonic generation has been observed in a periodically poled nonlinear optical polymer waveguide. Key elements in this demonstration include novel nonlinear optical polymers that can be spin coated, the design and fabrication of periodic electrodes for periodic poling and the optimization of waveguide parameters to obtain single-mode waveguides with a large overlap between fundamental and harmonic modes. Phase matching of the d33 nonlinear optical coefficient occurs over a distance L=230 μm.
Anisotropic etching of n+ polycrystalline silicon with high selectivity using a chlorine and nitrogen plasma in an ultraclean electron cyclotron resonance etcher
Authors: Uetake Hiroaki , Matsuura Takashi , Ohmi Tadahiro , Murota Junichi , Fukuda Koichi , Mikoshiba Nobuo
Published: July 2002

Heavily phosphorus-doped polycrystalline silicon films (n+ poly-Si) were etched in a pure chlorine plasma using an ultraclean electron cyclotron resonance etcher. Compared against undoped polycrystalline etching, horizontal etch rates were too high to allow anisotropic etching of n+ poly-Si. With the addition of more than about 10% N2, highly anisotropic etches of n+ poly-Si can be obtained simultaneously with selectivities as high as 160 to SiO2 in a 4 mTorr plasma. These results are significant to lower submicron fabrication. X-ray photoelectron spectroscopy studies show that Si—N bonds are formed on the n+ poly-Si surface during etching and it is proposed that this layer protects the sidewall against Cl radicals in a N2/Cl2 plasma. The suppression of SiO2 etching by O2 addition to a N2/Cl2 plasma has also been demonstrated.
One-dimensional magnetic flux microscope based on the dc superconducting quantum interference device
Authors: Mathai A. , Song D. , Gim Y. , Wellstood F. C.
Published: July 2002

We have designed and operated a magnetic flux microscope which measures the magnetic field above a sample surface by scanning a 4.2 K thin-film dc superconducting quantum interference device (SQUID) along one direction. With the SQUID and sample separated by about 160 μm, the system can image features with a spatial resolution of about 220 μm and a magnetic field resolution of 1.8×10−13 THz−1/2. We have used the system to view trapped magnetic flux, to image thin-film strips of superconducting Pb in field strengths of 0–750 nT, and to monitor the position of a sample with a resolution of approximately 0.5 nm Hz−1/2 at a frequency of 4 kHz.
Different types of pore structure in porous silicon
Authors: Parkhutik V. P. , Albella J. M. , Martinez-Duart J. M. , Gómez-Rodríguez J. M. , Baró A. M. , Shershulsky V. I.
Published: July 2002

A morphology of pores formed in silicon by its anodic polarization in a hydrofluoric acid has been studied using scanning tunneling microscopy (STM). The results obtained show that the pore structure, as yielded from the STM measurements, may be ordered or fibrouslike depending on the anodic current applied to obtain the porous silicon layers. This dependence is interpreted in terms of the theoretical model assuming the pore growth through a virtual passive layer formation at the pore bottoms and its dissolution.
Deposition of large area YBa2Cu3O7 superconducting films by laser scanning ablation
Authors: Song W. D. , An C. W. , Lu D. S. , Fan Y. C. , Li Z. G.
Published: July 2002

A method of laser scanning ablation for producing large area YBa2Cu3O7 superconducting films is presented. Uniformly thick, large area YBa2Cu3O7 superconducting films were obtained on 36-mm-diam (100) LaAlO3 substrates with a lens rotating radius of 9 mm. The Tc’s of the film center and edge were all 92 K and transition widths were less than 1 K. X-ray diffraction studies showed complete c-axis orientation of the films. The critical current density of 3.6×106 A/cm2 in zero field was measured at 77 K. A power law of voltage V versus current I of the YBa2Cu3O7 superconducting microbridge, V=1.363×10−32I11.224 49 was achieved.
Giant magnetoresistance in Fe/Cr superlattices with very thin Fe layers
Authors: Schad R. , Potter C. D. , Beliën P. , Verbanck G. , Moshchalkov V. V. , Bruynseraede Y.
Published: July 2002

Carefully tailored Fe/Cr epitaxial superlattices with extremely thin Fe layers have been grown on MgO(100) by molecular beam epitaxy. The low-angle x-ray spectra reveal the presence of sharp interfaces down to an Fe layer thickness of a few monolayers. An [Fe(4.5 Å)/Cr(12 Å)]50 superlattice shows a 220% magnetoresistance at 1.5 K, and a saturation field of 110 kOe. A further decrease of the Fe layer thickness produces a drastic decrease in the magnetoresistance.
Near-resonance acousto-optical interactions in GaAs and InP
Authors: Renosi P. , Sapriel J.
Published: July 2002

Acousto-optical properties of GaAs and InP are thoroughly investigated for photon energies tending to the band gap from below, and the whole set of photoelastic constants is determined as a function of the wavelength λ for λ≤1.06 μm. Figures of merit as high as 1200 times those of silica have been measured. It is shown how one can take advantage of the near-resonance acousto-optical properties of GaAs and InP in device design, in spite of the optical absorption. Such devices could be broadband, fast, compact, and insensitive to light polarization and may involve other direct-gap III-V crystals, adapted to the laser radiation.
Microstructured gold/Langmuir–Blodgett film/gold tunneling junctions
Authors: Fischer C. M. , Burghard M. , Roth S. , Klitzing K. v.
Published: July 2002

We prepared symmetric sandwich structures of the sequence gold/Langmuir–Blodgett film/gold by employing a novel evaporation technique. As molecular systems, we used an octasubstituted palladiumphthalocyanine and a perylene-3,4,9,10-tetracarboxyldiimide derivative. Electronic transport measurements show a tunneling characteristic which arises from a direct tunneling process through molecular states. The current/voltage curves are symmetric for positive and negative bias proving the identical electronic behavior of the two organic/inorganic interfaces at the top and bottom electrode.
An i
n s
i
t
u cell for transmission EXAFS measurements on catalytic samples
Authors: Kampers F. W. H. , Maas T. M. J. , van Grondelle J. , Brinkgreve P. , Koningsberger D. C.
Published: July 2002

An in situ cell suitable for transmission EXAFS measurements on catalytic samples is described. The cell can be used for catalyst pretreatments in various atmospheres (including H2, H2S, O2 and CO) in a temperature range upto 700 K. The sample is heated by conducting heat from an external heater to the sample. During measurement the samples can be cooled down to 77 K by conducting heat from the sample to an external liquid nitrogen container. During the pretreatment and the measurement a waterflow through the body of the cell keeps certain crucial parts from overheating or icing up. To avoid radiation leaks in powdery samples these samples are pressed in a selfsupporting wafer and held in a disk-shaped sampleholder. Tests by various catalytic groups have proven the suitability of the design.
Novel fabrication process of planar waveguides in rare-earth doped fluoroindate glasses
Authors: de Melo R. P. , da Silva B. J. P. , Falcão-Filho E. L. , da Silva E. F. , Petrov D. V. , de Araújo Cid B. , Messaddeq Y. , Aegerter M. A.
Published: July 2002

We report the successful fabrication of planar waveguides in rare-earth doped fluoroindate glass substrates. A new procedure for waveguide fabrication using a thermally evaporated AgF nonmetallic film was developed. The refractive index changes of more than 0.03, associated to low propagation losses achieved, open new perspectives and show the potentiality of using this glass family toward further developments in fabrication and design of integrated optical devices for optical communication wavelengths.
A phase-space-compressing, mass-selecting beamline for hyperthermal, focused ion beam deposition
Authors: Boyd Kevin J. , Łapicki Adam , Aizawa Masato , Anderson Scott L.
Published: July 2002

We have developed an ion beamline for hyperthermal ion-surface collisions that incorporates a phase-space compressor to improve the focusability/current density of the ion beam in the 1–10 eV deposition energy range. In essence, collisional damping is used to substantially improve the brightness of the ion source. In addition to the focusing behavior, the beamline also accomplishes mass selection, source-target pressure reduction of >1010, confinement of the beam to avoid space charge spreading, and hyperthermal energy beam transport. For our application the requirement is moderately tight (100 s of microns) focusing at hyperthermal energies (1–100 eV), but the principle should also be applicable to improving spot sizes/current densities at higher energies.
Use of focused ion beams for making tiny sample holes in gaskets for diamond anvil cells
Authors: Orloff Jon , Narayana Chandrabhas , Ruoff Arthur L.
Published: July 2002

To achieve multimegabar pressures in the diamond anvil cell, small diamond tips, 20 μm (or less) in diameter and high strength gasket materials are required. To prevent plastic instability it is therefore necessary to drill sample holes with diameters of 10 μm (or less) in extremely strong and tough materials such as tungsten. The present paper describes a technique for drilling such holes using focused ion beams. The superior roundness and surface finish of these holes is one of the reasons our group was able to reach pressures of 342 GPa on hydrogen, significantly higher than that reached by other researchers.
Measurement of the complex dielectric constant down to helium temperatures. I. Reflection method from 1 MHz to 20 GHz using an open ended coaxial line
Authors: Martens H. C. F. , Reedijk J. A. , Brom H. B.
Published: July 2002

The reflection off an open ended coaxial probe pressed against a material under test is used to determine the complex microwave (1 MHz–20 GHz) dielectric response of the material. A full-wave analysis of the aperture admittance of the probe, in terms of the dielectric properties of the backing material and the dimensions of the experimental geometry, is given. We discuss the calibration procedure of the setup and present the complex dielectric response of several materials determined from the measured reflection coefficient. The results obtained with the open ended coax interpolate well between data taken at lower and higher frequency bands using different experimental methods. We demonstrate that this method can be applied to perform dielectric measurements at cryogenic temperatures.
Alignment of InP Stranski–Krastanow dots by growth on patterned GaAs/GaInP surfaces
Authors: Seifert W. , Carlsson N. , Petersson A. , Wernersson L.-E. , Samuelson L.
Published: July 2002

Stranski–Krastanow islands of InP nucleate in straight rows when deposited by metalorganic vapor phase epitaxy on linearly patterned GaInP/GaAs surfaces. The patterns were produced by overgrowth of lithographically defined W stripes 30° off from [1̄10] on a GaAs(001) surface. Depending on the geometry of the grown GaAs/GaInP mesa stripes the islands were found to align either on top of the ridges, at the sidewall near to the mesa edge or at the bottom of the trenches. The highest density of almost equidistant coherent islands observed in some of the rows is in the order of 10 islands/μm, corresponding to a surface area density of 1010 InP islands/cm2. The maximum density of randomly distributed islands in the unpatterned area otherwise is only 2×109 islands/cm2. The results show a successful combination of overgrowth of conducting metal stripes and lateral geometrical positioning of dots in one in situ growth step.
Enhancement of the third-order nonlinear optical susceptibility in epitaxial vanadyl-phthalocyanine films grown on KBr
Authors: Fang Shaoli , Tada Hirokazu , Mashiko Shinro
Published: July 2002

We determined the magnitude of the third-order nonlinear optical susceptibilities χ(3)(−3ω; ω, ω, ω) of vanadyl-phthalocyanine (VOPc) films grown on KBr and fused silica substrates, using the third harmonic generation method at a wavelength of 1200 nm. The χ(3) value of the film grown epitaxially on KBr was 2.87×10−10 esu, which was greater by a factor of about 7.7 than that of a polycrystalline film grown on fused silica. The enhancement of χ(3) in the epitaxial phase is associated with the optimized orientation of the two-dimensional π-electron system in the condensed phase.
Compressively strained multiple quantum well InAsSb lasers emitting at 3.6 μm grown by metal-organic chemical vapor deposition
Authors: Lane B. , Wu D. , Rybaltowski A. , Yi H. , Diaz J. , Razeghi M.
Published: July 2002

A compressively strained InAsSb/InAs multiple quantum-well (MQW) structure was grown by low-pressure metal-organic chemical vapor deposition. Maximum output power (from two facets) up to 1 W with differential efficiency about 70% was obtained from a MQW laser with stripe width of 100 μm and cavity length of 700 μm for emitting wavelength of 3.65 μm at 90 K in pulse mode operation. About 2 times lower threshold current density was obtained from the MQW lasers for a temperature range of 90 to 140 K compared to the double heterostructure lasers grown on the same growth conditions.
Continuous wave ultraviolet frequency upconversion due to triads of Nd3+ ions in fluoroindate glass
Authors: Menezes L. de S. , de Araújo Cid B. , Maciel G. S. , Messaddeq Y. , Aegerter M. A.
Published: July 2002

We have observed ultraviolet upconversion fluorescence from the D3/24 and P3/22 levels of Nd3+ in fluoroindate glass under infrared pumping. It was found that the excitation of a large population in the F3/24 metastable level allows to achieve strong upconversion emissions at 354 and 382 nm. A simple rate equation model reproduces the temporal behavior of the upconverted emission and allows us to estimate the energy transfer rate among three Nd3+ ions participating in the process.
Atom-resolved scanning tunneling microscopy of vertically ordered InAs quantum dots
Authors: Wu Warren , Tucker John R. , Solomon Glenn S. , Harris James S.
Published: July 2002

We present cross-sectional scanning tunneling microscopy (STM) images of strain-induced, self-organized InAs quantum dots grown on GaAs. Samples containing 5 and 10 sequentially grown dot layers are investigated, and dots from different layers are seen to align in vertical columns. Our STM images are in general agreement with previous structural imaging, such as cross-sectional transmission electron microscopy, except that dot crowns appear more truncated. Although the size of the dots in most columns is roughly constant, monotonic changes in diameter are observed in some cases. STM analysis also reveals many new atom-resolved details of electronic structure, including dissolution of the InAs wetting layer and the presence of indium between the dot columns, which we attribute to segregation and diffusion of indium out of the wetting layer during overgrowth.
Millimeter-wave phase conjugation using artificial nonlinear surfaces
Authors: Chang Yian , Fetterman Harold R. , Newberg Irwin L. , Panaretos Steve K.
Published: July 2002

An artificial nonlinear surface has been developed using antenna-coupled mixers with optical interconnects for microwave and millimeter-wave phase conjugation. Prototype one-dimensional arrays have been constructed and have been used to demonstrate two-dimensional free-space phase conjugation at 10.24 GHz. The phase conjugation properties have been observed and verified by directly measuring the electric-field distribution of the conjugate wave under various conditions. Furthermore, the experiments have shown amplified conjugate wave power up to ten times of that of the incoming wave. This amplifying ability demonstrates the potential of such surfaces to be used in novel communications applications.
Observation of inhibited spontaneous emission and stimulated emission of rhodamine 6G in polymer replica of synthetic opal
Authors: Yoshino K. , Lee S. B. , Tatsuhara S. , Kawagishi Y. , Ozaki M. , Zakhidov A. A.
Published: July 2002

We report the observation of inhibited spontaneous emission of organic dye rhodamine 6G infiltrated in a polymer replica of synthetic opal as a photonic crystal. The morphology-dependent resonances, superimposed on the broadband emission of rhodamine 6G due to spherical wavelength-sized microcavity enhancement of dye emission, have also been observed.
Syntactic coalescence of WS2 nanotubes
Authors: Remškar M. , Škraba Z. , Sanjinés R. , Lévy F.
Published: July 2002

WS 2 nanoropes merged from nanotube coalescence present a new case of inorganic fiber composites with several nanotubes grown side by side up to a few millimeters in length. The extremities of external and inner spirally rolled-up molecular layer building the tubes are at the origin of the nanotube nucleation leading to the syntactic growth of nanotubes. The model of undulation of thin crystal flakes based on stacking mismatch is discussed. The nanoropes grow also by self-assembly or by coalescence of single tubes at low angles of incidence. An attractive long-range force leading to the nanotube approach is proposed.
Magnetic properties of annular Josephson junctions for radiation detection: Experimental results
Authors: Cristiano R. , Esposito E. , Frunzio L. , Lisitskii M. P. , Nappi C. , Ammendola G. , Barone A. , Parlato L. , Balashov D. V. , Gubankov V. N.
Published: July 2002

We report on experimental results about Josephson junctions for radiation detection with an annular geometry. The observed suppression of the critical Josephson current and the presence of one single resonance step in the current–voltage characteristic, as predicted by the theory, strongly support the idea that this geometry could be very convenient for radiation detection. The results were obtained when one single magnetic fluxon was trapped in the central hole, and they represent the first experimental confirmation of the theoretical predictions in the case of annular junctions with finite ring width.
Tunnel contact junction native-oxide aperture and mirror vertical-cavity surface-emitting lasers and resonant-cavity light-emitting diodes
Authors: Wierer J. J. , Kellogg D. A. , Holonyak N.
Published: July 2002

Vertical-cavity surface-emitting lasers (VCSELs) and resonant-cavity light-emitting diodes (RCLEDs) are demonstrated with high index contrast distributed Bragg reflectors (DBRs) on either side of a λ-thickness cavity (λ∼980 nm). The devices, with tunnel contact junctions making possible lateral electron current excitation, have a lower 6.5 period native-oxide-based AlxOy/GaAs DBR and an upper reflector that is either a 2–4 period AlxOy/GaAs DBR, a 1–2 period SiO2/ZnSe DBR, a λ/4-thickness layer of AlxOy (antireflecting), or no mirror at all. The AlxOy/GaAs DBRs and a buried-oxide-defined current aperture are formed by selective oxidation of the high Al composition AlxGa1−xAs layers. Device characteristics are observed as a function of the upper DBR periodicity (reflectivity). Devices with upper reflectivities of R≳99% operate as VCSELs while those with less reflectivity R≲96% operate as RCLEDs, some with external differential quantum efficiencies as high as η∼27% and narrow spectral emission (Δλ∼50 Å).
High power asymmetrical InAsSb/InAsSbP/AlAsSb double heterostructure lasers emitting at 3.4 μm
Authors: Wu D. , Lane B. , Mohseni H. , Diaz J. , Razeghi M.
Published: July 2002

Midinfrared lasers with an asymmetrical InPAsSb/InAsSb/AlAsSb double heterostructure are reported. Using the asymmetrical double heterostructure, p- and n-cladding layers are separately optimized; high energy-gap AlAsSb (Eg≈1.5 eV) for the p-type cladding layer to reduce the leakage current, and thus to increase To, and low energy-gap InPAsSb (Eg≈0.5 eV) for the n-cladding layer to have low turn-on voltage. 100-μm-width broad-area lasers with 1000 μm cavity length exhibited peak output powers of 1.88 W in pulse and 350 mW in continuous wave modes per two facets at T=80 K with To of 54 K and turn-on voltage of 0.36 V. Maximum peak output powers up to 6.7 W were obtained from a laser bar of total aperture of 400 μm width and cavity length of 1000 μm, with a differential efficiency of 34% and far-field beam divergence narrower than 40° at 80 K.