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Biomedical subjects

M Volk

Publications and source records attributed to M Volk.

At least 19 recordsLinked to original sources
PubMed2002

Interferometer-type structures for guided atoms.

We experimentally demonstrate interferometer-type guiding structures for neutral atoms based on dipole potentials created by microfabricated optical systems. As a central element we use an array of atom waveguides being formed by focusing a red-detuned laser beam with an array of cylindrical microlenses. Combining two of these arrays, we realize X-shaped beam splitters and more complex systems like the geometries for Mach-Zehnder and Michelson-type interferometers for atoms.

Journal Article↗
PubMed2002

Micro-optical realization of arrays of selectively addressable dipole traps: a scalable configuration for quantum computation with atomic qubits.

We experimentally demonstrate novel structures for the realization of registers of atomic qubits: We trap neutral atoms in one- and two-dimensional arrays of far-detuned dipole traps obtained by focusing a red-detuned laser beam with a microfabricated array of microlenses. We are able to selectively address individual trap sites due to their large lateral separation of 125 microm. We initialize and read out different internal states for the individual sites. We also create two interleaved sets of trap arrays with adjustable separation, as required for many proposed implementations of quantum gate operations.

Journal Article↗
PubMed2001

Efficient asymmetric epoxidation of alpha,beta-unsaturated ketones using a soluble triblock polyethylene glycol-polyamino acid catalyst.

[reaction: see text]. Polyethylene glycol (PEG)-bound poly-L-leucine acts as a THF-soluble catalyst for the Juliá-Colonna asymmetric epoxidation of enones. Excellent enantioselectivities may be obtained even with short chain length polyleucine. FT-IR investigations have determined that the catalytically active polyleucine components of these copolymers have an alpha-helical structure.

Journal Article↗
PubMed2001

The effect of Escherichia coli heat-stable toxin on the trans-epithelial intestinal elimination of ciprofloxacin in the rabbit.

The effect of Escherichia coli heat-stable toxin (ST) on the intestinal trans-epithelial elimination of ciprofloxacin was studied in the rabbit model. Following a systemic 27 mg/kg dose, excreted amounts of ciprofloxacin during the 2 h experiment were: 9.3 (+/- 4.8); 12.5 (+/- 5.2) and 0.3 (+/- 0.1) microg/cm(2) surface of intestinal wall in ST-challenged jejunal, ileal and caecal loops, respectively. In control loops the corresponding amounts were: 5.0 (+/- 2.8), 6.5 (+/- 3.4) and 0.3 (+/- 0.1) microg/cm(2), respectively. The trans-epithelial elimination of ciprofloxacin was significantly higher in ST-challenged small bowel loops than in controls while caecal elimination was negligible.

Animals↗
PubMed1999

Environmental fate of amitrole: influence of dissolved organic matter

In this study the environmental fate of amitrole in terrestrial and aquatic model ecosystems was investigated. Under aerobic conditions mineralization of amitrole is the main degradation pathway. The experiments revealed that the leaching behaviour is low in the presence or the absence of dissolved organic matter (DOM) despite the high water solubility due to a strong binding of amitrole to soil constituents. Under anaerobic conditions the addition of DOM increases the transport of amitrole in soil columns. The tests with water/sediment model ecosystems showed that the mineralization of amitrole is lower in comparison to aerobic soil experiments. Up to 80.6% of the applied 14C-labelled amitrole transfer into the sediment and about 1/3 of this amount formed bound residues, which are not extractable.

Journal Article↗
PubMed1998

EBV persistence in memory B cells in vivo.

Epstein-Barr virus establishes latency in vitro by activating human B cells to become proliferating blasts, but in vivo it is benign. In the peripheral blood, the virus resides latently in resting B cells that we now show are restricted to the sIgD memory subset. However, in tonsils the virus shows no such restriction. We propose that EBV indiscriminately infects B cells in mucosal lymphoid tissue and that these cells differentiate to become resting memory B cells that then enter the circulation. Activation to the blastoid stage of latency is an essential intermediate step in this process. Thus, EBV may persist by exploiting the mechanisms that produce and maintain long-term B cell memory.

B-Lymphocyte Subsets↗
PubMed1997

Application of a prognostic scoring system to critically ill patients in a small military facility.

Two hundred one consecutive adult admissions to a 3-bed Special Care Unit in a 25-bed military hospital were scored using APACHE II (Acute Physiology and Chronic Health Evaluation). Outcome measures included APACHE II scores and mortality predictions; active intensive care interventions; transfers for specialized care; and mortality. Although higher scores generally reflected the need for intensive care intervention, admissions with nondiagnostic chest pain had scores that did not accurately predict their course. This finding could be explained by bias in the original APACHE case mix and by the need for further subclassification of cardiovascular disease. APACHE II scoring can be applied in small intensive care settings. Scoring criteria and logistic regression equations may need to be customized accordingly.

APACHE↗
PubMed1995

Resurfacing of a large laryngeal wound with mucosa grafting: a combined technique using endoscopic suture and laser soldering.

Resurfacing of a large laryngeal wound has traditionally been accomplished via an open approach--transplanting free mucosa either onto the wound directly or upon a stent. This study proposes a new approach for wound resurfacing that combines endoscopic suturing with a laser welding technique. By means of a carbon dioxide (CO2) laser, a large (20 x 25 mm) defect in laryngeal mucosa involving the glottic and subglottic area was created in five dogs. Two of the animals served as controls and received no further treatment. In the remaining three animals the wound was resurfaced with buccal mucosal grafts fixed in place by standard suture placement and a technique of CO2 laser-assisted tissue soldering. The accessible edges of the graft were soldered endoscopically with human albumin-based tissue adhesive "activated" by low power (0.8 to 1.0 W) of a CO2 laser. All animals were examined endoscopically 1 week after surgery and sacrificed painlessly 4 weeks after surgery. The treated animals showed a viable mucosal graft with improved wound healing and voice function compared to that of the control animals. This new approach combines suture fixation of the inferior aspect of the mucosal graft, an area not well exposed endoscopically, and endoscopic laser soldering techniques for the repair of large laryngeal wounds.

Animals↗
PubMed1994

Metabolic relationship between the CO dehydrogenase molybdenum cofactor and the excretion of urothione by Hydrogenophaga pseudoflava.

Urothione was isolated as an excretion product of Hydrogenophaga pseudoflava and other bacteria at amounts approaching 253 micrograms/l of culture corresponding to 44 micrograms/g bacterial dry mass. The compound was identified as urothione by co-chromatography with urothione isolated from human urine, its characteristic ultraviolet and visible absorption spectra, oxidation to pterin-6-carboxylic-7-sulfonic acid by alkaline permanganate, 1H-NMR spectroscopy, double-quantum-filtered Fourier-transform 1H correlated spectroscopy, circular-dichroism spectroscopy and mass spectroscopy. A metabolic relationship between urothione and the carbon monoxide dehydrogenase molybdenum cofactor was suggested by a 1.1:0.5 molar ratio between urothione excreted and degradation of carbon monoxide dehydrogenase, a coincidence of urothione excretion and induction of carbon monoxide dehydrogenase with different species of carboxidotrophic bacteria, a structural relationship between molybdopterin cytosine dinucleotide of the carbon monoxide dehydrogenase molybdenum cofactor and urothione, and the demonstrated conversion of the carbon monoxide dehydrogenase molybdenum cofactor to urothione in vitro. A pathway for the conversion of the H. pseudoflava carbon monoxide dehydrogenase molybdenum cofactor to urothione has been proposed which involves molybdopterin cytosine dinucleotide, molybdopterin, phospho-norurothione and norurothione.

Aldehyde Oxidoreductases↗
PubMed1994

Coagulation profile as a predictor for post-tonsillectomy and adenoidectomy (T + A) hemorrhage.

The risk of hemorrhage after tonsillectomy and adenoidectomy (T + A) was studied in 1061 children. Twenty-seven (2.5%) had at least one abnormality on a preoperative coagulation profile consisting of a prothrombin time (PT), partial thromboplastin time (PTT), bleeding time (BT) and platelet count (PC). Of these 27 who had an initially abnormal test (PTT or bleeding times only), 8 had diagnosed coagulopathies by hematology evaluation (Group A), and 17 had repeat tests which returned to normal (Group B). Two borderline tests (PTT) were not repeated (Group C). Sixty-four patients (6.0%) bled after T + A. Six of these (9.3%) had an initially abnormal coagulation profile--one in Group A (12.5%), four in Group B (23.5%) and 1 in Group C (50%). This is in contrast to the bleed rate of 5.7% for the 1034 children with normal coagulation profiles. Although it is not surprising that 6 (22.2%) children with an initially abnormal coagulation profile bled, of note is that 4 of them had an initially abnormal coagulation profile which upon repeat testing returned to normal. However, none of these four bleeders required active intervention for control. Coagulopathies were newly diagnosed in 7 (0.57% of total group; 25.9% of 27 with abnormal laboratory values). One additional child had a known intrinsic platelet dysfunction prior to surgery. Only one child was newly identified by a positive family history for abnormal bleeding. These results suggest that new hematologic disorders were diagnosed infrequently. An initially abnormal coagulation profile may identify those more likely to bleed after surgery (22.6% vs. 5.5%). A coagulation profile which includes a PTT and BT may be a valuable screening tool for children undergoing T + A.

Adenoidectomy↗
PubMed1994

[Transposition of the fallopian tube as a therapeutic possibility in special cases of tubal sterility].

This is a report on a new method of microsurgical transposition of the Fallopian tube. It was developed to deal with congenital malformations or with the different anatomic remnants after pelvic surgery or pelvic inflammatory diseases. The tube is mobilised by severing the mesosalpinx with the unipolar microelectrode without damaging the longitudinal vessels. After mobilisation, the bends of the tube disappear and the length increases almost doublefold. Then the tube can be laid to the contralateral ovary without any tension. The tube must be fixed to the ovary in such a way, that the fimbrial end is mobile enough to lay onto the ovary during ovulation. Up to now, six patients with longstanding tubal sterility were operated upon. Three of them became pregnant, one twice. There were no ectopic pregnancies and no abortions.

Adult↗
PubMed1993

Similarity of primary radical pair recombination in photosystem II and bacterial reaction centers.

We report temperature and magnetic field dependent measurements of the recombination dynamics of the radical pair P680+Pheo- in D1D2cytb559 reaction centers of photosystem II and compare the results to those obtained in bacterial reaction centers. In photosystem II the rate of recombination to the groundstate is found to be slower than in the bacterial reaction centers by a factor of at least 50. This difference arises from the different redox potentials of the pigments of plant and bacterial reaction centers. In contrast, the rate of recombination to the triplet state is similar in all reaction centers, indicating a similar electronic coupling which allows us to conclude upon the structural similarity.

Chlorophyll↗
PubMed1993

Needle aspiration of peritonsillar abscess in children.

Needle aspiration for the treatment of peritonsillar abscess was assessed in 43 consecutive children aged 7 to 18 years (mean age, 13.9 +/- 2.5 years) during the 3-year period from 1988 through 1991. A positive aspirate was obtained in 31 (76%) of the 41 patients who cooperated for needle aspiration; a mean of 2.9 +/- 1.9 mL of pus was withdrawn. Of the 31 children with a positive aspirate, in 27 (87%) the abscess resolved, two (6%) required a second aspiration for resolution, and two (6%) underwent immediate tonsillectomy for persistent abscess. Of the 10 children (24%) with negative aspirations, in six (60%) the abscess resolved with antibiotic treatment alone, three (30%) underwent immediate (quinsy) tonsillectomy, and in one (10%) the abscess spontaneously drained. No bleeding, airway obstruction, or anesthetic complications occurred. Needle aspiration of peritonsillar abscess in children, with tonsillectomy reserved for nonresponders, appears to be an efficacious and safe method of treatment.

Adolescent↗
PubMed1992

Influence of time and osmolarity on nuclear area of tumor cells growing in vitro.

We investigated the simultaneous influence of the time of cultivation and of the osmolarity of the medium on nuclear sizes in vitro. Cells from a permanent cell line (MaTu), derived from a human breast cancer, were used. We found a linear increase of nuclear size during the first 64 h in culture. In contrast to the important influence of time on nuclear size in culture, even distinct variations of the osmolarity of the medium had little influence on nuclear size. Only if the osmolarity rose by 28% was there a clear reduction of nuclear size.

Breast Neoplasms↗
PubMed1992

Needle aspiration of neck abscesses in children.

Needle aspiration of neck abscesses with CT-scan guidance was studied in 17 children with 18 abscesses from 1986 to 1991. Clinical and radiologic findings were analyzed according to treatment outcome. A majority of abscesses (55.6%) resolved after treatment with one to two attempts at needle aspiration and parenteral antibiotics. Unilocular abscesses were more likely than multilocular abscesses to resolve with needle aspiration. In general, abscesses in younger children who presented with smaller neck masses on physical examination and smaller abscess cavities on CT scan resolved with needle aspiration. The data support the use of needle aspiration as an effective initial treatment for pediatric neck abscesses. CT scan was found beneficial in documenting the abscesses and in guiding treatment. A treatment protocol is suggested for the use of needle aspiration in the management of neck abscesses in children.

Abscess↗
PubMed1991

The relationship of tonsil bacterial concentration to surface and core cultures in chronic tonsillar disease in children.

Fifty-five tonsils removed for chronic tonsillar disease (chronic tonsillitis and obstructive tonsillar hyperplasia) underwent surface swab and quantitative core cultures in order to identify the relationship between core bacterial concentration and the presence of aerobic bacteria on the tonsil surface. The accuracy of a single core culture was further established by quantitative cultures of 9 sections per tonsil in an additional 19 tonsils. The results indicate that many (61.5%) but not all aerobic bacteria which were found in the tonsil core were cultured from the surface of the tonsil. Conversely, the tonsil core bacteria with the highest bacterial concentrations are more likely to be present on the tonsillar surface and the greater the bacterial concentration, the more likely the bacteria are to be found in most if not all areas of the tonsil core. Therefore, the core bacterial concentration appears to be related to the presence of aerobic bacteria on the tonsillar surface. Surface bacteria may not, however, be truly representative of the core bacterial environment. Implications for the management of chronic tonsillar disease will be discussed.

Bacteria↗
PubMed1991

Term pregnancy after fallopian tube transposition.

A 23-year-old woman suffered from primary sterility because of congenital malformation of the uterus and tubes. There was a left unicornuate uterus. The left ovary and the isthmic and ampullary parts of the right tube were missing. Microsurgical transposition of the left tube was performed successfully. Our technique may encourage microsurgeons to use transposition of fallopian tube in cases in which only one tube and one ovary on contralateral sides are available.

Adult↗