Growth of Low-Density Vertical Quantum Dot Molecules with Control in Energy Emission

In this work, we present results on the formation of vertical molecule structures formed by two vertically aligned InAs quantum dots (QD) in which a deliberate control of energy emission is achieved. The emission energy of the first layer of QD forming the molecule can be tuned by the deposition of controlled amounts of InAs at a nanohole template formed by GaAs droplet epitaxy. The QD of the second layer are formed directly on top of the buried ones by a strain-driven process. In this way, either symmetric or asymmetric vertically coupled structures can be obtained. As a characteristic when using a droplet epitaxy patterning process, the density of quantum dot molecules finally obtained is low enough (2 × 10⁸ cm⁻²) to permit their integration as active elements in advanced photonic devices where spectroscopic studies at the single nanostructure level are required.     

A Fully Automated Process Using a Magnetic Particle Based Kit for Removal of Dye Terminators from Sequencing Reactions

Prolinx,® Inc. of Bothell, WA has developed the RapXtract™ 384 Dye Terminator Removal Kit for full automation of DNA sequencing reaction purification. The RapXtract product line is based upon proprietary superparamagnetic particle technology that eliminates the need for centrifugation, vacuum filtration, or modified primers to achieve purification of sequencing reactions. The kit described here is pre-dispensed in a 384-well microtiter plate and run on the TECAN GENESIS Workstation 150 (Tecan U.S. Inc., Research Triangle Park, NC). This system enables rapid purification of up to 384 sequencing reactions in a single run.As the completion of the Human Genome Project nears, it is imperative for biotechnology and pharmaceutical companies to increase throughput of DNA sequencing in order to be competitive in the drug discovery and validation process. The “race to market” requires a shift from standard DNA sequencing processes-including DNA sequencing reaction purification-towards complete walk-away automation for all steps.Existing sequencing reaction purification methods (Table 1) require considerable resources including: plastic and other laboratory consumables; specialized equipment, such as high-speed centrifuges or vacuum filtration apparatus; and labor-intensive protocols requiring large amounts of technician time. As a result, walk-away automation of standard purification methods is difficult and expensive.     

Capital market development and mass privatization are logical contradictions: lessons from Russia and the Czech Republic

The introduction of mass privatization policies in Russia andthe Czech Republic depended on the creation of impersonal capitalmarkets to finance the needs of privatized companies and toprovide a secondary market for the trading of securities. Yet,mass privatization created the contradictory conditions of generatingmillions of poorly informed shareholders, with no efficientmarkets for the sale of the shares. The absence of financialmarkets created systematic pressures to move assets by illegalor non-transparent means to users who value them more. Privatizationcreated the incentives to destroy the financial markets criticalto its success. A comparative case analysis of post-privatizationmarket formation in both these countries demonstrates that thefunctional necessity for these markets does not engender theirown creation. In the absence of institutional mechanisms ofstate regulation and trust, markets become arenas for politicalcontests and economic manipulation. The irony of these policiesis that a principal lesson has been that market reforms cannotcreate viable markets, only institutional formation can.     

An investigation of the effects of material anisotropy and heterogeneity on pulsed, laser-generated acoustic signals

Point-source and line-source models for the laser ultrasonic source in materials exhibiting transverse isotropy are applied to the specific problem of laser generation and ultrasonic propagation in unidirectional, polymer matrix composite materials. Comparing experiment and theory, it is shown that these composite materials exhibit homogeneous behavior, at the frequencies investigated, for ultrasonic wave propagation perpendicular to the fiber direction. For ultrasonic propagation in the fiber direction, ultrasonic dispersion, resulting from the inhomogeneous nature of the composite, affects the laser ultrasonic signal.     

In vitro translation of a 2.3-kb splicing variant of the hamster pgp1 gene whose presence in transfectants is associated with decreased drug resistance

Adherent macrophage populations derived from monocytes isolated from peripheral blood were evaluated for their ability to "shed" the membrane-associated receptor for TNF-alpha (TNFR) following exposure to a calcium ionophor (A23187) and a synthetic chemotactic peptide (fMLP) reagent. A soluble fraction of TNFR was detected in "cell-free" supernatant produced by stimulated macrophage populations applying 125I-TNF-alpha and biotinylated TNF-alpha ligand-binding analysis (96-well format) in combination with conventional autoradiographic techniques. Approximate molecular weight of the shed TNFR glycoprotein fraction was estimated to be 75 kDa based on interpretation of nondenaturing PAGE gels transferred laterally onto sheets of nitrocellulose membrane subsequently probed by ligand-binding analysis applying 125I-TNF-alpha and biotinylated TNF-alpha as detection modalities. Immunorecognition techniques were also employed to detect TNFR fragments shed from macrophages using biotinylated anti-TNFR Type II (75 kDa) monoclonal antibody in combination with conjugated strepavidin:HRPO and a chemiluminescent substrate reagent. In an effort to identify the class of enzyme directly mediating TNFR Type II (75 kDa) shedding, a spectrum of carboxyl- (e.g., aspartate), hydroxyl- (e.g., serine), thiol (e.g., cysteine), and metalo- (e.g., Ca2+, Mg2+) protease-inhibiting agents were evaluated. Experimental findings implied that a carboxy (aspartate) peptidase, and possibly to a lesser extent, serine (hydroxyl), and thiol (cysteine) peptidases participate in macrophage TNFR Type II (75 kDa) shedding phenomena. Subsequent investigations demonstrated that the carboxy (aspartate) peptidase cathepsin-D promoted liberation of TNFR Type II (75 kDa) in unactivated populations of adherent macrophages. In an effort to complement these observations, a protein fraction with presumed carboxy (aspartate) protease activity was isolated from the cell-free supernatant generated by activated populations of adherent macrophages using immobilized pepstatin-A beaded agarose. Exposure of unstimulated populations of adherent macrophages to the partially purified pepstatin-A binding protein fractions resulted in the liberation of a soluble TNFR Type II (75 kDa) fragment based on interpretation of ligand-binding and immunorecognition analysis of samples developed by SDS-PAGE/PAGE format and transferred onto sheets of nitrocellulose membrane. The molecular weight of the macrophage pepstatin-A binding protein fraction was estimated to be 47-52 kDa with lesser bands also visible at approximately 26-32 kDa, and 100 kDa based on SDS-PAGE analysis. Nondenaturing hemoglobin-PAGE substrate gel analysis of protein fractions possessing pepstatin-A binding-avidity detected a protease with a molecular weight of approximately 47-52 kDa that proteolytically digested hemoglobin, in addition to a synthetic cathepsin-D specific peptide substrate. Collective interpretation of these experimental findings directly corresponds with many of the physical (molecular) and functional (biochemical) characteristics known to be associated with the leukocyte carboxy (aspartate) peptidase cathepsin-D, which is a non-metaloprotease known to exert relatively limited proteolytic activity.     

Coding mammograms using the classification "probably benign finding--short interval follow-up suggested"

OBJECTIVE: Many benign breast lesions revealed by mammography show features indicating that the lesions have a high, but not complete, likelihood of being benign. The Breast Imaging Reporting and Data System (BI-RADS) allows radiologists to classify these mammograms as "probably benign finding-short interval follow-up suggested" (category 3). We explored whether certain factors are associated with the use of category 3 in a national cancer detection program. MATERIALS AND METHODS: We analyzed data from the National Breast and Cervical Cancer Early Detection Program, a comprehensive nationwide program that provides cancer screening for low-income and medically underserved women. The study population included all women at least 40 years old who had undergone mammography on or before September 30, 1996 (n = 372,760). RESULTS: Of the 372,760 mammograms, 7.7% were classified as category 3. The probability of receiving a category 3 classification decreased as patients' ages increased. Women who were symptomatic were nearly twice as likely as women who were asymptomatic to receive a category 3 classification, and women whose clinical breast examinations had abnormal findings were more than twice as likely as women with examinations having normal findings to receive a category 3 classification. The percentage of mammograms classified as category 3 by state or tribal organization ranged from 1.4% to 14.0%. CONCLUSION: Several patient variables, including patient symptomatology, were associated with the probability of having a mammogram classified as category 3. One of the most important determinants was where the patient underwent mammography, which suggests that variability exists among radiologists themselves in using this BI-RADS code for "probably benign" mammographic lesions.     

The effectiveness of early endoscopy for upper gastrointestinal hemorrhage: a community-based analysis

OBJECTIVES: The effectiveness of upper endoscopy in unselected patients with upper gastrointestinal hemorrhage has not been well studied. This study was undertaken to identify factors associated with the performance of early endoscopy (ie, within 1 day of hospitalization) and, after adjusting for these factors, to determine associations between early endoscopy and in-hospital mortality, length of stay, and performance of surgery. METHODS: Subjects in this observational cohort study were 3,801 consecutive admissions with upper gastrointestinal hemorrhage to 30 hospitals in a large metropolitan region. Demographic and clinical data were abstracted from hospital records. A multivariable model based on factors that potentially could relate to the decision to perform endoscopy was developed to determine the propensity (0 to 100%) for early endoscopy in each patient. RESULTS: Early endoscopy was performed in 2,240 patients (59%), and although it was not associated with mortality after adjusting for severity of illness among all patients, it was associated with a higher risk of death for patients in the lowest propensity group. Early endoscopy was associated with a lower likelihood of upper gastrointestinal surgery in all patients and in the two highest propensity groups and with a shorter length of stay in the entire cohort and in all subgroups. CONCLUSIONS: In the absence of specific contraindications, early endoscopy should be considered because of associated reductions in length of stay and surgical intervention. Further studies are needed to identify subgroups in whom the procedure may be associated with adverse effects on survival.     

Laboratory investigation of the mass stability of sampling cassettes from inhalable aerosol samplers

A study was conducted to evaluate the mass stability of the materials used in the construction of samplers with internal cassettes for the gravimetric measurement of inhalable aerosol exposures. The internal cassettes from IOM samplers were studied. Results indicate that the mass stability of filters is uniform, but the mass stability of the cassette material may dramatically affect the results of the measurement. Cassettes constructed from plastic exhibited drastic shifts in mass depending on the environmental conditions of their storage. Under room humidity, the plastic cassettes absorbed 1 to 2 mg of water over several days. When these cassettes were placed in a desiccator, they lost mass consistently but did not approach a stable mass. Studies repeated with cassettes made of stainless steel showed negligible mass variability. Based on this study, the use of stainless steel cassettes is recommended for gravimetric determinations of aerosol exposure, although field blanks may in some cases be used for correction of data from plastic cassettes. This study shows the need to evaluate the mass stability of the cassette material of any sampling device where an internal cassette is weighed together with the filter.     

Surface topography of phytochrome A deduced from specific chemical modification with iodoacetamide

Phytochromes are a photoreversible photochromic light switch for photomorphogenesis in plants. The molecular structure and functional mechanism of phytochromes are not fully understood. On the basis of complete mapping of total tryptic digest of the iodoacetamide-modified oat phytochrome A (phyA), the molecular surface topography of phyA was probed by specific chemical modification of cysteine residues with [14C]iodoacetamide. Under native conditions, only two cysteines (Cys-158 and Cys-311) of eleven half-cystines of the N-terminal chromophore binding domain were modified to a significant extent. In the C-terminal domain, six cysteine residues (Cys-715, Cys-774, Cys-809, Cys-869, Cys-961, Cys-995) were readily accessible to iodoacetamide. Among the reactive cysteine residues, only cysteine-311 displayed reactivity that was dependent on the photochromic form (Pr left arrow over right arrow Pfr) of the photoreceptor. Surprisingly, the modification of Cys-311 in the vicinity of the chromophore attachment site (Cys-321) did not have any detectable effect on spectral properties of phyA. Most of the cysteines of the N-terminal domain (Cys-83, Cys-175, Cys-291, Cys-370, Cys-386, Cys-445, Cys-506) are deeply buried in the core of the chromophore binding domain, as they can be modified only after denaturation of the chromoprotein. In the C-terminal domain, modification of only one cysteine residue (Cys-939) required protein denaturation. Since all 22 half-cystines can be modified with iodoacetamide without reduction of the chromoprotein, it follows that oat phyA does not have any disulfide bonds. We found that Cys-311, Cys-774, Cys-961, and Cys-995 could be easily partially oxidized under the conditions used for phytochrome isolation. The surface topography/conformation of oat phyA and its role in protein-protein recognition in phytochrome-mediated signal transduction are discussed in terms of the relative reactivity of cysteine residues.