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H Blok

Publications and source records attributed to H Blok.

13 recordsLinked to original sources
PubMed2005

Plasmon-assisted two-slit transmission: Young's experiment revisited.

We present an experimental and theoretical study of the optical transmission of a thin metal screen perforated by two subwavelength slits, separated by many optical wavelengths. The total intensity of the far-field double-slit pattern is shown to be reduced or enhanced as a function of the wavelength of the incident light beam. This modulation is attributed to an interference phenomenon at each of the slits, instead of at the detector. The interference arises as a consequence of the excitation of surface plasmons propagating from one slit to the other.

Journal Article↗
PubMed2005

High-frequency EPR and ENDOR spectroscopy on semiconductor nanocrystals.

EPR and ENDOR experiments at 95 GHz on ZnO nanoparticles reveal the presence of shallow donors related to interstitial Li and Na atoms. The experiments allowed, for the first time, to probe the effect of confinement on the shape of the electronic wave function. In addition, it is observed that the 67Zn nuclear spins become polarized upon saturation of the EPR transition. This Overhauser effect is induced by the zero-point vibrations of the phonon system in the nanoparticles.

Journal Article↗
PubMed2005

ENDOR spectroscopy at 275 GHz.

A pulsed ENDOR spectrometer operating at a microwave frequency of 275 GHz is described. The results demonstrate that this type of spectroscopy can now be performed routinely at this high microwave frequency. The advantages compared to conventional EPR frequencies are the high spectral resolution, time resolution, and sensitivity.

Journal Article↗
PubMed2004

A continuous-wave and pulsed electron spin resonance spectrometer operating at 275 GHz.

An electron paramagnetic resonance (EPR) spectrometer is described which allows for continuous-wave and pulsed EPR experiments at 275 GHz (wavelength 1.1 mm). The related magnetic field of 9.9 T for g approximately 2 is supplied by a superconducting solenoid. The microwave bridge employs quasi-optical as well as conventional waveguide components. A cylindrical, single-mode cavity provides a high filling factor and a high sensitivity for EPR detection. Even with the available microwave power of 1 mW incident at the cavity a high microwave magnetic field B1 is obtained of about 0.1 mT which permits pi/2-pulses as short as 100 ns. The performance of the spectrometer is illustrated with the help of spectra taken with several samples.

Carbon↗
PubMed2002

Costs associated with a strict policy to eradicate methicillin-resistant Staphylococcus aureus in a Dutch University Medical Center: a 10-year survey.

Although the Dutch policy to eradicate methicillin-resistant Staphylococcus aureus (MRSA) is very strict compared to policies employed in other countries, it has proven to be successful epidemiologically (incidence of MRSA in the Netherlands, <0.5%). The present study was performed to investigate both the financial and the logistical consequences of this strict, so-called "search and destroy" policy in the Netherlands. The data were based on a 10-year survey (1991-2000) of screening, surveillance, and outbreaks at the University Medical Center Utrecht. The consequences of the policy were determined by a panel comprising physicians from the Department of Surgery, the Department of Medical Microbiology, Subdivision Hospital Hygiene and Infection Prevention, the Department of Pharmacy, and Household Services. The costs associated with the policy were also calculated, including those for additional (disposable) material, cultures, specific medication, decontamination, and closing of the wards. Over the course of the 10 years, implementation of the MRSA policy resulted in more than 2,265 lost hospitalization days. In addition, the wards had to be closed 48 times, 29 healthcare workers had to temporarily discontinue working, and 78,000 additional cultures had to be performed. The total cost reached 6 million Dutch guilders (euro 2,800,000). The financial and logistical consequences were then compared to those in a hypothetical situation without the "search and destroy" policy. In such a situation, the hospital would be faced with an increased incidence of MRSA, vancomycin intermediate-susceptible Staphylococcus aureus, and vancomycin-resistant enterococci. The costs associated with the use of alternative antibiotics, required in a scenario of high endemic-level MRSA, would be at least twice as high as the costs expended in the actual situation, thus demonstrating that a strict MRSA policy is financially worthwhile.

Academic Medical Centers↗
PubMed2002

Comparison of two surveillance methods for detecting nosocomial infections in surgical patients.

Nosocomial infections play a role in quality and cost control in health care. Surveillance of these infections is the only way to gain more insight into their frequency and causes. Since the results of surveillance may lead to changes in both patient and hospital management, which are sometimes major, it is necessary that all healthcare workers involved agree on the criteria used for the diagnosis and surveillance of these complications. In order to compare the efficacy of two surveillance methods, nosocomial infections in surgical patients were registered by both the Department of Surgery (complication surveillance [CS]) and the Department of Infection Control (nosocomial infection surveillance [NIS]) at the University Medical Center Utrecht, The Netherlands, over a 2-month period. The CS team used the national criteria of the Association of Surgeons of the Netherlands and the NIS team used the international criteria of the Centers for Disease Control and Prevention, USA, to define cases of nosocomial infection. A total of 515 patients were included in both arms of the study. The CS team diagnosed 69 infections in 49 patients, and the NIS team diagnosed 64 infections in 45 patients. Of 104 total infections, 39 were diagnosed by the CS team exclusively, 35 by the NIS team exclusively and only 30 by both. The main reasons for the inconsistent results were as follows: (i) the lack of follow-up after discharge in the NIS arm, (ii) the use of clinical criteria for the definition of a nosocomial infection in the CS arm, and (iii) the use of positive cultures as part of the criteria in the NIS arm. From the perspective of infection control, the CS system cannot be recommended for the surveillance of nosocomial infections.

Centers for Disease Control and Prevention, U.S.↗
PubMed2001

Five-year surveillance of patients with communicable diseases nursed in isolation.

During a five year surveillance program of patients with communicable diseases nursed in isolation, we gathered information on 2880 patients who were nursed in isolation for 28 145 days, from January 1994 to December 1998. The mean number of patients nursed in isolation was 575.4 (range, 427-709) per year. On average 2.4% of patients admitted yearly to the University Medical Center (UMC) were nursed in isolation. The mean number of days nursed in isolation was 9.8 days per patient.1996 was a peak year in isolations due to outbreaks of gentamicin-resistant enterobacteriaceae (GRB) and methicillin resistant Staphylococcus aureus (MRSA). The main reasons for requiring isolation were: GRB, MRSA (proven and suspected cases), Clostridium difficile, viral infections and Mycobacterium tuberculosis. Registration of quantitative data on nursing patients in isolation, as presented in this paper, makes it possible to gain insight into the type and number of isolation indications, the required isolation room capacity on different wards, the workload of healthcare workers resulting from isolation and the trends in incidence of communicable diseases.

Communicable Diseases↗
PubMed1999

The High Throughput Screening Infrastructure: The Right Tools for the Task.

HTS is a key component of pharmaceutical lead identification process. Over recent years, the pharmaceutical industry has experienced significant increases in the throughput capabilities of its HTS functions. In those companies where HTS has been effectively deployed, it is now possible to screen the entire corporate compound collection against a pharmacological target within a timescale of several weeks to a few months. This capability has been realized, not as a result of the purchase of any one particular piece of hardware, but rather through the development of a truly effective HTS infrastructure that matches the needs of the parent organization. Central to this is the need to understand how to effectively combine the use of the different types of hardware available to the HTS specialist. The use of both modular workstations and single-arm robotic systems have underpinned most HTS groups operations. Recent advances in the field of multiple-arm robotic systems and dedicated automation systems offer even further potential for increasing productivity. This article describes our experience with the use of a dedicated automation system for HTS applications.

Journal Article↗
PubMed1999

Stacker Modules Used in a High-Capacity Robotics System for High Throughput Screening Compound Replication.

High throughput screening is now established as a key component of the pharmaceutical lead identification process in many pharmaceutical companies. Over recent years, thanks to advances in assay technology, process automation, and logistics control, the throughput capacity of HTS groups has increased significantly. It is now entirely possible to screen corporate compound collections against an individual pharmacological target within a timescale of several weeks. Despite these improvements, many HTS groups find that their capacity is limited by the rate at which they can provide test compounds in a "screen-ready" format. This limitation is usually imposed by the capacity and productivity of the single-armed robotic systems utilized. We have recently constructed a robotic system aimed at overcoming this particular problem. This system uses purpose-built microplate stacker units that provide high-capacity microplate storage and, importantly, provide an easy and fast interface between the robotic system and the human operators. This paper describes this automation project and the benefits that have resulted from its deployment.

Journal Article↗
PubMed1993

Quantification of central benzodiazepine receptor binding potential in the brain with 123I-iomazenil SPECT: technical and interobserver variability.

Factors contributing to the quantification of the central benzodiazepine receptor binding potential in vivo using 123I-iomazenil and single photon emission computed tomography (SPECT) were analysed in phantom studies and in volunteers. SPECT was performed with the SME810 multidetector system. The Hoffman three-dimensional brain phantom was used to investigate linearity and reproducibility of SPECT results using different 123I activity concentrations. Dynamic and multislice SPECT scans were performed in nine healthy volunteers between 0 and 270 min after injection of 110 MBq 123I-iomazenil. Displacement studies were performed in three volunteers using 1 mg flumazenil administered intravenously (i.v.) at 250 min postinjection (p.i.). Regions of interest (ROIs) over the cerebral cortex and various subcortical nuclei were either fixed areas based on a stereotaxic brain atlas, or manually drawn, based on 60% isocontour lines. Interobserver variability of the ROI data and ratios derived from those data were estimated for two independent observers. The brain phantom measurements showed linearity with respect to 123I concentration and good reproducibility. The interobserver study showed a reasonable interobserver reliability for the large fixed ROIs. The displacement study showed about 50% displacement in all ROIs. Concentrations of 123I-iomazenil in the brain can be measured reliably with the SME810. Large fixed ROIs based on a stereotaxic atlas may be used reliably for quantification. The level of 4 cm above the cantomeatal line does not provide a useful reference region with a very low central benzodiazepine receptor binding potential.

Adult↗
PubMed1986

Class-specific antibody determination against Aspergillus fumigatus by means of the enzyme-linked immunosorbent assay. III. Comparative study: IgG, IgA, IgM ELISA titers, precipitating antibodies and IgE binding after fractionation of the antigen.

IgG, IgA and IgM ELISA antibody titers against Aspergillus fumigatus were elevated in sera of patients with aspergilloma and allergic bronchopulmonary aspergillosis (ABPA), showing higher titers for the IgG antibodies compared with the IgA and IgM antibodies. No differences were found between titers of identical antibody classes in the two groups of sera. IgG and IgA ELISA titers were highly specific whereas IgM ELISA showed more unspecific binding of IgM antibodies. Antibodies, as measured by ELISA, studied after fractionation of the antigen into fractions of decreasing molecular weight, showed a preferential binding by the high molecular weight fractions. Precipitating antibodies studied in patient sera did not always correspond with the IgG ELISA titers. IgE antibody binding was observed in all fractions from Sephadex G-100 fractionated components; maximum binding was found with fractions of 28,000-60,000 daltons. The low molecular weight fractions (18,000-less than 5,000 daltons) showed less IgE binding but the quantity of this fraction was higher. The discrepancies noted between the IgG and IgA ELISA titers and the binding of IgM or IgE antibodies indicate that antigenic components may in part differ in the binding of antibody classes.

Antibodies, Fungal↗