PubMed Health⌕ Search

Biomedical subjects

S Burger

Publications and source records attributed to S Burger.

At least 19 recordsLinked to original sources
PubMed2005

Optical microscopy via spectral modifications of a nanoantenna.

The existing optical microscopes form an image by collecting photons emitted from an object. Here we report on the experimental realization of microscopy without the need for direct optical communication with the sample. To achieve this, we have scanned a single gold nanoparticle acting as a nanoantenna in the near field of a sample and have studied the modification of its intrinsic radiative properties by monitoring its plasmon spectrum.

Journal Article↗
PubMed2005

Magnetic metamaterials at telecommunication and visible frequencies.

Arrays of gold split rings with a 50-nm minimum feature size and with an LC resonance at 200 THz frequency (1.5 microm wavelength) are fabricated. For normal-incidence conditions, they exhibit a pronounced fundamental magnetic mode, arising from a coupling via the electric component of the incident light. For oblique incidence, a coupling via the magnetic component is demonstrated as well. Moreover, we identify a novel higher-order magnetic resonance at around 370 THz (800 nm wavelength) that evolves out of the Mie resonance for oblique incidence. Comparison with theory delivers good agreement and also shows that the structures allow for a negative magnetic permeability.

Journal Article↗
PubMed2001

Expansion of a coherent array of Bose-Einstein condensates.

We investigate the properties of a coherent array containing about 200 Bose-Einstein condensates produced in a far detuned 1D optical lattice. The density profile of the gas, imaged after releasing the trap, provides information about the coherence of the ground-state wave function. The measured atomic distribution is characterized by interference peaks. The time evolution of the peaks, their relative population, as well as the radial size of the expanding cloud are in good agreement with the predictions of theory. The 2D nature of the trapped condensates and the conditions required to observe the effects of coherence are also discussed.

Journal Article↗
PubMed2001

Josephson junction arrays with Bose-Einstein condensates.

We report on the direct observation of an oscillating atomic current in a one-dimensional array of Josephson junctions realized with an atomic Bose-Einstein condensate. The array is created by a laser standing wave, with the condensates trapped in the valleys of the periodic potential and weakly coupled by the interwell barriers. The coherence of multiple tunneling between adjacent wells is continuously probed by atomic interference. The square of the small-amplitude oscillation frequency is proportional to the microscopic tunneling rate of each condensate through the barriers and provides a direct measurement of the Josephson critical current as a function of the intermediate barrier heights. Our superfluid array may allow investigation of phenomena so far inaccessible to superconducting Josephson junctions and lays a bridge between the condensate dynamics and the physics of discrete nonlinear media.

Journal Article↗
PubMed2001

Superfluid and dissipative dynamics of a Bose-Einstein condensate in a periodic optical potential.

We create Bose-Einstein condensates of 87Rb in a static magnetic trap with a superimposed blue-detuned 1D optical lattice. By displacing the magnetic trap center we are able to control the condensate evolution. We observe a change in the frequency of the center-of-mass oscillation in the harmonic trapping potential, in analogy with an increase in effective mass. For fluid velocities greater than a local speed of sound, we observe the onset of dissipative processes up to full removal of the superfluid component. A parallel simulation study visualizes the dynamics of the Bose-Einstein condensate and accounts for the main features of the observed behavior.

Journal Article↗
PubMed2000

Diagnostic errors in three medical eras: a necropsy study.

BACKGROUND: Studies comparing the accuracy of clinical diagnosis in unselected patients who died in hospital in different medical eras have shown no decline of errors in the main diagnosis. We assessed changes in diagnostic accuracy over 20 years. METHODS: We analysed retrospectively diagnostic errors, with use of necropsy as the gold standard for diagnosis. We randomly selected 300 patients who died at a tertiary-care teaching hospital in Switzerland--100 in each of 1972, 1982, and 1992. We classified discrepancies between clinical diagnosis and necropsy findings as major and minor errors. FINDINGS: The overall necropsy rate at the hospital stayed at around 90% for the whole period. During the study, the frequency of major discrepancies declined significantly (1972, 30%; 1982, 18%; 1992, 14%; p=0.007). The rate of minor diagnostic errors increased significantly from 23% in 1972 to 46% in 1992 (p<0.001). The increase in overall diagnostic accuracy occurred mainly because of a significant improvement in specificity for cardiovascular diseases (1972, 85%; 1982, 82%; 1992, 97%; p=0.034) and non-significantly improved sensitivity (1972, 69%; 1982, 82%; 1992, 86%; p=0.061). Sensitivity also improved for infectious diseases (1972, 25%; 1982, 67%; 1992, 86%; p=0.036). Sensitivity and specificity for neoplastic diseases were high originally and did not change. The total number of diagnostic procedures per year increased from 191 in 1972 to 259 in 1992, mainly because of non-invasive techniques, such as ultrasonography, and endoscopies. INTERPRETATION: The frequency of major diagnostic errors in unselected patients who died in hospital was halved over 20 years, probably because of improved clinical skills and new diagnostic procedures.

Aged↗
PubMed2000

Experts recommend minimum nurse staffing standards for nursing facilities in the United States.

The experts concluded that current data show that the average nurse staffing levels (for RNs, LVN/LPNs, and NAs) in nursing homes are too low in some facilities to provide high quality of care. Caregiving, the central feature of a nursing home, needs to be improved to ensure high quality of care to residents. Because detailed time studies have not been conducted on the amount of time that is required to provide high quality of care to residents, expert opinion is currently the best approach to addressing the problem of inadequate staffing. Increases in the education level and training of nursing staff are also strongly recommended as a step to improving quality of care and reducing turnover rates in nursing homes. These recommendations are designed for consideration by Congress, HCFA regulators, policymakers, nursing home administrators, and nurses. Ideally, Congress would pass legislation establishing these recommendations as minimum standards for all nursing homes or direct HCFA to establish detailed minimum nurse staffing standards to ensure that staffing levels take into account the number and the case-mix of the residents. Alternatively, HCFA could introduce minimum staffing standards through the regulatory process. In 1999 there were a number of efforts at the state level to increase minimum staffing levels. Mohler (1999) surveyed selected states and found that 21 states had either proposed new legislation or were considering proposals for new legislation or new regulations. In California, for example, in 1999 the state budget approved $31 million in new state funds (to be matched with $31 million in federal Medicaid dollars) to increase nursing home staffing minimum requirements from 2.8 to 3.2 hr per resident day and to increase wage rates. Overall, nursing facilities need to be held accountable by HCFA for providing adequate levels and types of staffing to meet the needs of their residents, especially because government is paying for 61% of the expenditures. Adopting these minimum standards will have an important impact on improving the quality of the nation's nursing home care. Additional research is needed to determine appropriate levels and types of staff to provide high quality of care to residents. These studies could test the proposed staffing standards against existing staffing levels to examine the impacts on quality. As new data become available on staffing levels, revisions of staffing standards should be made if necessary to ensure that high standards are maintained.

Aged↗
PubMed2000

A nurse-led, unit-based program to reduce restraint use in acute care.

Although the effectiveness of restraints is not proven, the dangers of restraints are clear. Many advocate for the reduction of restraint use in tertiary care settings. The Joint Commission on the Accreditation of Healthcare Organizations is setting the standard by insisting that hospital administrations create a culture that emphasizes restraint reduction. Despite the importance of this task, very little is available in the literature to direct or guide this effort. The purpose of this article is to describe a unit-based Restraint Reduction Program that was successful on a neurology/neurosurgery unit.

Academic Medical Centers↗
PubMed1998

Developing patient and family education services. Innovations for the changing healthcare environment.

As the healthcare environment changes, systems that have served hospitals well for many years no longer meet the current needs of patients, families, and communities. This is particularly true with regard to health education. The authors describe an innovative learning center that offers comprehensive health education services and programs designed to empower consumers with the information and skills needed to maintain health or recover from illness or injury.

Boston↗
PubMed1997

Retroviral transduction of peripheral blood leukocytes in a hollow-fiber bioreactor.

BACKGROUND: Peripheral blood white cells (leukocytes) (PBLs) have been used as effective targets for genetic manipulation by transduction with retroviruses in open systems. A semi-closed hollow-fiber bioreactor was tested for culturing and transducing lymphocytes. STUDY DESIGN AND METHODS: PBLs were isolated from five healthy donors, and 5 x 10(7) cells were cultured in hollow-fiber bioreactors for 4 days after stimulation with anti-CD3 in medium containing 200 units per mL of recombinant interleukin 2. Transduction with retroviral vector containing the gene for iduronate-2-sulfatase and G 418 resistance, L2SN, was performed daily on Days 4, 5, 6, and 7, and the cells were expanded for an additional 3 days. RESULTS: PBLs from three donors were harvested from the bioreactor after transduction and expansion, and 4.5 x 10(9), 7.0 x 10(9), and 2.9 x 10(9) cells were recovered, representing 90-, 136-, and 58-fold expansions. The transduction frequency of L2SN was 10, 5, and 1 percent, respectively. For additional expansion of PBLs, in two cases the bioreactor was reinoculated with 5 x 10(7) cells, which were expanded again for 16 and 8 days, respectively, yielding 1.4 x 10(9) and 3.1 x 10(9) cells, which reflected an additional 28- and 62-fold expansion of cells. PBLs from two other donors were transduced and expanded in the bioreactor, and then 0.8 mg per mL of G 418 was added to the medium in an attempt to enrich the transduced population. Although 2.5 and 10 percent of the cells were transduced, cell death and absence of expansion in the presence of G 418 resulted in final cell lots with viabilities of only 4 and 8 percent. In all cases, the harvested cells tested negative in bacterial and fungal cultures. CONCLUSION: Hollow-fiber bioreactors are an efficient and effective system for the retroviral transduction and expansion of PBLs for clinical gene therapy.

Bioreactors↗
PubMed1997

[Medical rehabilitation between sociopolitical requirements and political employment market interests].

Due to the demographic development and the changes in morbidity, the medical rehabilitation in the statutory pension insurance will be more and more important in future. The budgeting of expenditures is not an appropriate means for the elimination of existing insufficiencies related to medical rehabilitation. Excessive or insufficient use of these services can be interpreted as moral hazard problems. The focus of all measures has to be to eliminate the existing disincentives in the interface between pension insurance and labor market in order to increase the efficiency of medical rehabilitation.

Aged↗
PubMed1996

BCR/ABL-negative primitive progenitors suitable for transplantation can be selected from the marrow of most early-chronic phase but not accelerated-phase chronic myelogenous leukemia patients.

We have previously reported that selection of marrow cells on the basis of the CD34+HLA-DR- phenotype (34+DR-) may result in the recovery of Philadelphia chromosome (Ph)- and BCR/ABL-negative long-term culture-initiating cells (LTC-IC) in selected patients with chronic myelogenous leukemia (CML). We now present data on 27 early chronic-phase ([ECP] studied within 1 year after diagnosis) and 23 advanced-phase ([AP] late chronic phase, ie, studied >1 year from diagnosis, or accelerated phase) CML patients. Fluorescence-activated call-sorting (FACS)-selected 34+DR- and 34+DR+ cells were subjected to reverse transcriptase-polymerase chain reaction and fluorescence in situ hybridization. These cells were also cultured in long-term bone marrow culture for 1 to 5 weeks to examine the number of LTC-IC and the presence or absence of the BCR/ABL gene rearrangement in progeny of primitive LTC-IC. The number of 34+DR- cells and LTC-IC present in ECP CML marrow was similar to that in normal (NL) marrow, whereas the numbers were reduced in AP CML. Furthermore, 34+DR- cells from more than 80% of ECP CML patients were BCR/ABL mRNA- and Ph-negative and contained only BCR/ABL mRNA- and Ph-negative LTC-IC, whereas 34+DR- cells and LTC-IC from less than 40% of AP CML patients were BCR/ABL mRNA- and Ph-negative. In contrast to NL marrow, 34+DR+ cells from CML marrow, irrespective of clinical stage, contained large numbers of LTC-IC. CML 34+DR+ cells and LTC-IC were BCR/ABL mRNA- and Ph-positive. Since these studies suggested that a population of primitive progenitors that are Ph-negative can be selected from steady-state marrow in some ECP CML patients, we determined if similar results could be obtained when large quantities of marrow sufficient for transplantation are processed. We demonstrate that 1 to 3 x 10(5) BCR/ABL mRNA-negative 34+DR- cells/kg recipient body weight, containing only BCR/ABL mRNA-negative LTC-IC, can be obtained from a 2- to 2.5-L marrow collection by sequential COBE Spectra apheresis (COBE BCT, Lakewood, CO), CD34+ enrichment using the CEPRATE SC Cell-Concentrator (CellPro, Bothell, WA), and high-speed FACS. Thus, large-scale selection of a BCR/ABL mRNA- and Ph-negative 34+DR- cell population is possible in a fraction of chronic-phase CML patients, in whom these cells could be used to reconstitute the hematopoietic compartment following autologous transplantation.

Antigens, CD34↗
PubMed1996

Production of fruits and vegetables at the homestead is an important source of vitamin A among women in rural Bangladesh.

BACKGROUND: Vitamin A deficiency is considered to be an important public health problem in Bangladesh. A universal biannual distribution of high-dose vitamin A capsules has been in place for over the past two decades. This supplementation has been beneficial for preschool children. Bangladesh has been exploring more sustainable approaches for all segments of the population. To support this initiative, Helen Keller International has implemented a homegardening promotion project since 1993. This project is executed on a large scale and currently reaches an estimated 244,000 families. METHODS: This paper presents data from 7341 women of reproductive age which were collected as part of the baseline census of a community monitoring system whose objective is to track progress and measure the impact of home-gardening activities. RESULTS: Vitamin A intake in this population derived almost entirely from the consumption of fruits and vegetables. Logistic regression analyses showed that maternal vitamin A intake was determined by qualitative indicators of homestead gardens (type of home garden, the total quantity of provitamin A-rich food produced and the number of fruits and vegetables varieties grown in the garden) after adjusting for socio-economic status. CONCLUSIONS: These results indicate that traditional production of provitamin A-rich fruits and vegetables in the homestead may provide a valuable contribution to vitamin A intake in communities where alternative dietary sources of vitamin A are scarce.

Agriculture↗
PubMed1994

Primary structure of maize chloroplast adenylate kinase.

This paper describes the sequence of adenylate kinase (Mg-ATP+AMP<-->Mg-ADP+ADP) from maize chloroplasts. This light-inducible enzyme is important for efficient CO2 fixation in the C4 cycle, by removing and recycling AMP produced in the reversible pyruvate phosphate dikinase reaction. The complete sequence was determined by analyzing peptides from cleavages with trypsin, AspN protease and CNBr and subcleavage of a major CNBr peptide with chymotrypsin. N-terminal Edman degradation and carboxypeptidase digestion established the terminal residues. Electrospray mass spectrometry confirmed the final sequence of 222 residues (M(r) = 24867) including one cysteine and one tryptophan. The sequence shows this enzyme to be a long-variant-type adenylate kinase, the nearest relatives being adenylate kinases from Enterobacteriaceae. Alignment of the sequence with the adenylate kinase from Escherichia coli reveals 44% identical residues. Since the E. coli structure has been published recently at 0.19-nm resolution with the inhibitor adenosine(5')pentaphospho(5')adenosine (Ap5A) [Müller, C. W. & Schulz, G. E. (1992) J. Mol. Biol. 224, 159-177], catalytically essential residues could be compared and were found to be mostly conserved. Surprisingly, in the nucleotide-binding Gly-rich loop Gly-Xaa-Pro-Gly-Xaa-Gly-Lys the middle Gly is replaced by Ala. This is, however, compensated by an Ile-->Val exchange in the nearest spatial neighborhood. A Thr-->Ala exchange explains the unusual tolerance of the enzyme for pyrimidine nucleotides in the acceptor site.

Adenylate Kinase↗
PubMed1991

Long-term stability of treatment results in cleft lip and palate patients.

The stability of the orthodontic and prosthetic results of the treatment of 18 individuals with isolated cleft of the palate, 18 subjects with a complete unilateral and 8 with a complete bilateral cleft was evaluated in an eight-year follow-up period. The subjects were examined at the age of 19 years, after completed orthodontic and surgical treatment, and again at the age of 27 years. After the first examination the majority of the individuals with a complete cleft had at the age of 20 to 21 years been treated with a fixed bridge which was only minimally extended. The width of the upper dental arch at the second bicuspid decreased slightly in the subjects with an isolated cleft of the palate and in those with a bilateral cleft. In the subjects with a unilateral cleft there was a slight decrease of the upper dental arch widths at both bicuspids and at the first molar. In the subjects with complete clefts the slight decrease in upper dental arch widths was accompanied by a slight increase of the number of posterior teeth in cross-bite. The total number of teeth in cross-bite was small, however. On the whole, the upper dental arch was relatively stable during the follow-up period. This was found in the group with bilateral clefts, reconstructed with 5-8 unit bridges, as well as in the subjects with a unilateral cleft who had received no or only minimally extended reconstructions and in the group with an isolated cleft of the palate (no bridge).

Adolescent↗
PubMed1988

Two regions within the human IL-2 gene promoter are important for inducible IL-2 expression.

We have examined regulatory domains of the human IL-2 gene promoter by transfection and transient expression of rDNA constructs in which the chloramphenicol acetyl transferase gene shows T cell-specific inducible expression and cyclosporin A-mediated inhibition when placed downstream of 587 bp of the human IL-2 5'-flanking region. A series of 5'-deletion constructs transfected into the Jurkat T lymphoid line demonstrates that a region encompassing 370 bp 5' of the transcription start site is sufficient for inducible chloramphenicol acetyl-transferase expression. Further dissection of this region with internal deletion (linker-scanner) mutants revealed that portions of at least two discrete regions from -42 to -169 and -289 to -361 bp relative to the transcription start site are critical for inducible expression of the IL-2 gene. T cell-specific expression of wild-type and mutant IL-2 promoter constructs could be increased severalfold by the insertion of an upstream SV40 enhancer. With use of a battery of IL-2 promoter constructs, we could not identify subregions within IL-2 5'-flanking sequences which are crucial for cyclosporin A inhibition of the IL-2 gene or deletion of which resulted in loss of T cell-specific expression, suggesting that such functions may be mediated at pre-transcriptional levels.

Acetyltransferases↗