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W Haase

Publications and source records attributed to W Haase.

At least 19 recordsLinked to original sources
PubMed2006

Orbital angular momentum contribution to the magneto-optical behavior of a binuclear cobalt(II) complex.

We report magnetic and magnetic circular dichroism investigations of a binuclear Co(II) compound. The Hamiltonian of the system involves an isotropic exchange interaction dealing with the real spins of cobalt(II) ions, spin-orbit coupling, and a low-symmetry crystal field acting within the (4)T(1g) ground manifold of each cobalt ion. It is shown that spin-orbit coupling between this ground term and the low-lying excited ones can be taken into consideration as an effective g factor in the Zeeman part of the Hamiltonian. The value of this g factor is estimated for the averaged experimental values of Racah and cubic ligand field parameters for high-spin cobalt(II). The treatment of the Hamiltonian is performed with the use of a irreducible tensor operator technique. The results of the calculation are in good agreement with experimental observations. Both a large effective g factor for the ground state and a large temperature-independent part of the magnetic susceptibility arise because of a strong orbital contribution to the magnetic behavior of the Co(II) dimer.

Circular Dichroism↗
PubMed2005

High frequency hysteresis-free switching in thin layers of smectic-C* ferroelectric liquid crystals.

The insulating layers used for the alignment of ferroelectric liquid crystals (FLC) in electro-optical cells usually have non-negligible thickness and their capacitance determines the type of the director switching caused by a triangular-form external voltage U(tr) . With decreasing frequency of U(tr) , the hysteresis in a switching direction changes from the normal to the abnormal one at a characteristic hysteresis inversion frequency f(i) . In the vicinity of f(i) , the electro-optical response is thresholdless and the optical transmission manifests the V -shape field dependence. The V -shape regime is very interesting for certain applications, in particular to microdisplays due to a possibility of the gray scale realization. However, f(i) has to be enhanced from the usually observed frequency of a few Hz up to the range of hundreds of Hz. To this effect, a special FLC material has been designed and its basic properties (tilt angle, spontaneous polarization, rotational viscosity, and electric conductivity) have been measured over the entire range of the smectic-C* phase. Upon variation of cell parameters (thickness of both the FLC and alignment layers), temperature, and external voltage, the frequency of the V -shape effect as high as 150-1000 Hz (in the temperature range 30-75 degrees C) has been found experimentally. The operating voltage remains lower than 8 V. A quantitative interpretation of these results has been done using the modeling procedure developed earlier [S.P. Palto, Cryst. Rep. 48, 124 (2003)]. The modeling has been performed with the experimental values of the FLC material and the cell parameters and has shown very good agreement with experiment. The key point of this approach is consideration of the internal voltage on the FLC layer, the sign, amplitude, and form of which differ from U(tr) . The results of the modeling allow further improvement of the performance of electro-optical FLC cells for high frequency V-shape effect.

Journal Article↗
PubMed2003

[Comparative examination between an angle stable, monokortikal osteosynthesis technique with the conventional plate osteosynthesis at the anterior arm shaft fracture].

With a retrospective Follow-up essay under the use of Matched peer variables the wellbeing course was examined by patient pairs (128 patients) assigned to 64 individually with fractures of the anterior arm shaft. A group which treats others with 2.7 or 3.5 mm DCP/LC-DCP got with the AO Point Contact basic gate (PC-Fix). The well-being course data count after the implantation on a period of 18 months. The Follow-up-rate was 100% for this time period. The patients became for each other on reason of the criteria: assigned to fracture classification, soft partial loss, accompanying injuries and age. Possible complications were: implantation conditional nerve damages, infections, implant failures, delayed healings, pseudarthroses, motion reductions and synostoses. Complications appeared (PC-Fix at 13 patients: respect, DCP: 5). The statistical testing didn't yield any statistically significant advantage for one for the two implants at a p-value of 0.5811 for.

Adult↗
PubMed2003

[Development of dynamic stereopsis after eye muscle operations for binocular vision impairment].

BACKGROUND: Strabism usually impairs central stereopsis irreversibly after a short time duration,however, the retinal periphery is more resistant to deterioration by binocular impairment. METHODS: In this prospective study 46 strabismic patients (9-56 years old) were tested for dynamic stereopsis in the peripheral visual field up to 20 degrees eccentricity. The effect of realignment of the visual axes by surgery on dynamic stereopsis was tested before and after surgery in 40 out of these patients. Patients were tested qualitatively for dynamically stereoactive fields of vision and quantitatively for the threshold value needed to create a three-dimensional impression. RESULT: We found residual dynamic stereopsis in 30% of patients without central static stereopsis: 56% of the patients improved after surgery, either through a significant (p<0.01) gain of stereoactive fields or through a decrease of threshold values. CONCLUSION: Strabismus surgery has benefits for the patients outside classical tests and seems to be independent of the static depth perception.

Adolescent↗
PubMed2002

"Thresholdless" hysteresis-free switching as an apparent phenomenon of surface stabilized ferroelectric liquid crystal cells.

The thresholdless, hysteresis-free V-shape electro-optical switching in surface-stabilized ferroelectric liquid crystals, observed usually with a triangular voltage form, has been shown to be rather an apparent and not a real effect. Strictly speaking, it is observed only at one characteristic frequency f(i) and is accompanied by an inversion of the electro-optical hysteresis direction from the normal to the abnormal one. The switching of the director in a liquid crystal layer at f(i), in reality, has a threshold and a normal hysteresis. Even the optical transmittance shows a hysteresis at f(i) when it is plotted as a function of the voltage on the liquid crystal layer and not as a function of the total voltage on the liquid crystal cell which always includes the inner insulating layers. Due to these layers, a voltage divider is formed which includes the capacitance of the insulating layers and the dynamic impedance (capacitance and resistance) of the ferroelectric liquid crystal layer. The new explanation has been confirmed by experiments with different ferroelectric liquid crystal cells combined with external resistors and capacitors and by measurements of a strong dependence of f(i) on the liquid crystal resistance which was varied over three orders of magnitude. A theoretical analysis of the problem has also been made using certain approximations for material parameters and the space dependence of the sine form of the electric field in the liquid crystal layer. The conclusions are qualitatively consistent with the experimental results. Finally, the dynamic problem has been solved numerically by taking into account of all the relevant parameters (in the absence of flow and irregularities in the cell plane) and the obtained results are in excellent correspondence with the experiment. This has been demonstrated for sets of material and cell parameters providing the best V-shape performance.

Journal Article↗
PubMed2002

Synthesis and structural characterization of trinuclear Cu(II)-pyrazolato complexes containing mu(3)-OH, mu(3)-O, and mu(3)-Cl ligands. Magnetic susceptibility study of [PPN](2)[(mu(3)-O)Cu(3)(mu-pz)(3)Cl(3)].

The nine-membered [-Cu(II)-N-N-](3) ring of trimeric copper-pyrazolato complexes provides a sturdy framework on which water is twice deprotonated in consecutive steps, forming mu(3)-OH and mu(3)-O species. In the presence of excess chlorides the mu(3)-O(H) ligand is replaced by two mu(3)-Cl ions. The interconversion of mu(3)-OH and mu(3)-O and the exchange of mu(3)-O(H) and mu(3)-Cl are reversible, and the three species involved have been structurally characterized: [PPN][Cu(3)(mu(3)-OH)(mu-pz)(3)Cl(3)(thf)].CH(2)Cl(2) (1a), monoclinic P2(1)/n, a = 10.055(2) A, b = 35.428(5) A, c = 15.153(2) A, beta = 93.802(3) degrees, V = 5386(1) A(3), Z = 4; [Bu(4)N][Cu(3)(mu(3)-OH)(mu-pz)(3)Cl(3)] (1b), triclinic P-1, a = 9.135(2) A, b = 13.631(2) A, c = 14.510(2) A, alpha = 67.393(2) degrees, beta = 87.979(2) degrees, gamma = 80.268(3) degrees, V = 1643.2(4) A(3), Z = 2; [PPN](2)[Cu(3)(mu(3)-O)(mu-pz)(3)Cl(3)] (2), monoclinic P2/c, a = 12.807(2) A, b = 13.093(2) A, c = 23.139(4) A, beta = 105.391(3) degrees, V = 3741(1) A(3), Z = 2; [PPN](2)[Cu(3)(mu(3)-Cl)(2)(mu-pz)(3)Cl(3)].0.75H(2)O.0.5CH(2)Cl(2) (3a), triclinic P-1, a = 14.042(2) A, b = 23.978(4) A, c = 25.195(4) A, alpha = 76.796(3) degrees, beta = 79.506(3) degrees, gamma = 77.629(3) degrees, V = 7988(2) A(3), Z = 4; [Bu(4)N](2)[Cu(3)(mu(3)-Cl)(2)(mu-pz)(3)Cl(3)] (3b), monoclinic C2/c, a = 17.220(2) A, b = 15.606(2) A, c = 20.133(2) A, beta = 103.057(2) degrees, V = 5270(1) A(3), Z = 4; [Et(3)NH][Cu(3)(mu(3)-OH)(mu-pz)(3)Cl(3)(pzH)] (4), triclinic P-1, a = 11.498(2) A, b = 11.499(2) A, c = 12.186(2) A, alpha = 66.475(3) degrees, beta = 64.279(3) degrees, gamma = 80.183(3) degrees, V = 1331.0(5) A(3), Z = 2. Magnetic susceptibility measurements show that the three copper centers of 2 are strongly antiferromagnetically coupled with J(Cu-Cu) = -500 cm(-1).

Journal Article↗
PubMed2001

Magnetic, spectroscopic, and structural studies of dicobalt hydroxamates and model hydrolases.

The cobalt(II) urease model complex [Co(2)(mu-OAc)(3)(urea)(tmen)(2)][OTf] (2) prepared from the cobalt model hydrolase [Co(2)(mu-H(2)O)(mu-OAc)(2)(OAc)(2)(tmen)(2)] (1) undergoes facile reaction with acetohydroxamic acid (AHA) to give the monobridged hydroxamate complex [Co(2)(mu-OAc)(2)(mu-AA)(urea)(tmen)(2)][OTf]( )()(3) while 1 gives the dibridged hydroxamate complex [Co(2)(mu-OAc)(mu-AA)(2)(tmen)(2)][OTf] (4). The structures and Co-Co distances of the hydroxamate derivatives of 1 and 2 are very close to those of their nickel analogues and suggest that hydroxamic acids can also inhibit cobalt-based hydrolases as well as inhibiting urease. 1 also reacts with glutarodihydroxamic acid (gluH(2)A(2)) to eliminate hydroxylamine with formation of [Co(2)(mu-OAc)(2)[mu-O(N) (OC)(2)(CH(2))(3)](tmen)(2)][OTf] (5), the structure of which is very close to that of its nickel analogue. Both 1 and 3 show weak antiferromagnetic coupling. Oxidation of 1 with H(2)O(2) gives three dicobalt(III) hydroxy complexes (7-9), the first of which [Co(2)(mu-OAc)(2)(OAc)(2)(mu-OH)(tmen)(2)][OTf] (7) contains a bridging hydroxyl and the second [Co(2)(mu-OAc)(2)(OAc)(mu-OH)(OH)(tmen)(2)][OTf] (8) containing both a bridging and terminal hydroxyl, while the third [Co(2)(mu-OAc) (OAc)(2)(mu-OH)(2)(tmen)(2)][OTf] (9) contains two bridging OH groups with mixed-valence Co(II)/(Co(III) intermediates.

Algorithms↗
PubMed2001

Dielectric investigation of electrically oriented ferroelectric smectic mixture CS-1013.

From dielectric spectroscopic study, a first-order ferroelectric phase transition has been observed in ferroelectric smectic mixture CS-1013 having the phase sequence Cr-SmC*-SmA-N*-Iso. Frequency (100 Hz-10 MHz) and temperature-dependent dielectric measurements have been performed on an electrically aligned sample (thickness 15+/-1 microm) gold coated on glass plates. In the unidirectionally aligned sample, two dielectric relaxation modes (Goldstone mode and soft mode) have been clearly observed in the ferroelectric SmC* phase while only one relaxation mode (soft mode) is visualized in the paraelectric SmA phase. Low-frequency molecular relaxation was also observed in the smectic phases. The experimental results have also been analyzed at different temperatures and biasing voltages for an understanding of the dynamics of dielectric processes in the ferroelectric phase. Finally, we proposed the "pseudospin" model for understanding the ferroelectric-antiferroelectric transition in liquid crystals. We associate the tilt angle straight theta and the pitch of the helix, respectively, with biaxial (b) and uniaxial (u) anisotropy parameters as fluctuating parameters around their stability limit (corresponding to the crystalline values). Here, the director acts as the pseudospin variable. This gives rise to a transverse Ising type (or anisotropic Heisenberg model under the mean-field approximation). It is then shown that such a model with fluctuations of (b) and (u) would explain the ferroelectric and antiferroelectric phase transitions in such liquid crystals. Using Landau theory and the stability conditions, we have also shown, in brief, the feasibility of different types of phase transitions in the ferroelectric liquid crystal system.

Journal Article↗
PubMed2001

Strong cooperativeness in the mononuclear iron(II) derivative exhibiting an abrupt spin transition above 400 K.

The spin crossover system, [Fe(bzimpy)(2)](ClO(4))(2).0.25H(2)O, was reinvestigated above room temperature (bzimpy = 2,6-bis(benzimidazol-2-yl)pyridine). The system exhibits an abrupt low-spin to high-spin transition at T(c) = 403 K. Liberation of a fractional amount of water does not affect the spin crossover: the system is perfectly reversible with a hysteresis width of DeltaT = 12 K. The existence of the hysteresis at such high temperature determines that the lowest limit of the solid-state cooperativity parameter is J/k > 403 K despite long iron(II) separations (10 A). The high cooperativeness has been assigned to a perfect pi-stacking of the benzimidazole rings in the crystal lattice at a distance as short as 3.6 A. Variable-temperature IR data and the heat capacity measurements match well the magnetic data. The thermodynamic properties are DeltaH = 17 kJ mol(-)(1), DeltaS = 43 J K(-)(1) mol(-)(1), so that the entropy of the spin transition shows a considerable contribution from the molecular vibrations. A theoretical model has been applied in fitting the magnetic data along the whole hysteresis path. A statistical distribution of the cooperativity parameter led to the feature that angled walls of the hysteresis loop are well reproduced.

Journal Article↗
PubMed2001

Synthesis, mesomorphism, and unusual magnetic behaviour of lanthanide complexes with perfluorinated counterions.

Lanthanide complexes of the Schiff base ligand 4-dodecyloxy-N-hexadecyl-2-hydroxybenzaldimine and with perfluorinated alkyl sulfate counterions were synthesised. All of the metal complexes show a smectic A mesophase. The viscosity of this mesophase is much lower than that of analogous compounds with nitrate or alkyl sulfate counterions. The behaviour of these new highly anisotropic molecular magnetic materials was studied using high-temperature X-ray measurements in an external magnetic field and temperature-dependent magnetic susceptibility measurements. The mu(eff)-versus-temperature curve is more comparable with those expected for nematic phases than for smectic phases. The luminescence spectrum of a EuIII compound shows that the values of the second rank crystal field parameters are very large. The huge magnetic anisotropy can be related to this strong crystal-field perturbation.

Journal Article↗
PubMed2001

[Effects on depth perception and pattern recognition in random dot stereograms by changing the matrix dot density].

INTRODUCTION: Julesz named the ability of depth perception in random dot stereograms as "global stereopsis". At present there are only high-density random dot stereograms with different disparities in use in the ophthalmological practice. The aim of our exploration is to measure the effects on pattern recognition and depth perception by thinning out the dot density in random dot stereograms down to very low levels (< 1%). METHODS: Experiments were performed by 43 volunteer observers using two sequences of random dot stereograms. Each sequence has its own constant disparity and within a sequence the dot density decreased to values less than 1%. Additionally we compared the performance in these tests with the performance in the conventional haploscopic stereoscopic tests (Titmus, TNO, Randot). RESULTS: Of the observers 48.8% (n = 21) were able to establish a complete depth perception and pattern recognition ("global stereopsis") at a matrix dot density of 0.3% and a disparity of 730" (12, 17'). Another group of subjects (48.8%, n = 21) saw the sub-matrix at 0.3% dot density in depth as a star field ("local stereopsis") but was not able to recognise the form of the sub-matrix. A significant correlation does not exist between these results and those from the conventional stereoscopic test. DISCUSSION: We assume from these results that the very low density random dot stereograms measure a new quality of stereoscopic vision, from which we can obtain information about the density of cortical binocular activated elements in the human brain.

Adolescent↗
PubMed2001

Analysis of a putative voltage-gated prokaryotic potassium channel.

Most of the completely sequenced prokaryotic genomes contain genes of potassium channel homologues, but there is still not much known about the role of these proteins in prokaryotes. Here we describe the large-scale overproduction and purification of a prokaryotic voltage-gated potassium channel homologue, Kch, from Escherichia coli. After successful overproduction of the protein, a specific increase in the potassium permeability of the cells was found. Kch could be purified in large amounts using classical purification methods to prevent aggregation of the protein. The physiological state of the protein was revealed to be a homotetramer and the protein was shown to be localized to the cytoplasmic membrane of the cells. In the course of the localization studies, we found a specific increase in the density of the cytoplasmic membrane on Kch production. This was linked to the observed increase in the protein to lipid ratio in the membranes. Another observed change in the membrane composition was an increase in the cardiolipin to phosphatidylglycerol ratio, which may indicate a specific cardiolipin requirement of Kch. On the basis of some of our results, we discuss a function for Kch in the maintenance of the membrane potential in E. coli.

Cell Membrane↗
PubMed2000

Radiation therapy for benign diseases: patterns of care study in Germany.

BACKGROUND: Radiotherapy of benign diseases is controversial and rarely applied in Anglo-American countries, whereas in other parts of the world it is commonly practiced for several benign disorders. Similar to a European survey, a patterns of care study was conducted in Germany. METHOD: Using a mailed questionnaire, radiation equipment, treatment indication, number of patients, and treatment concepts were assessed in 1994, 1995, and 1996 in 134 of 152 German institutions (88%): 22 in East and 112 in West Germany; 30 in university hospitals and 104 in community hospitals. Average numbers of each institution and of all institutions were analyzed for frequencies and ratios between regions and among institutions. Radiation treatment concepts were analyzed. RESULTS: A mean of 2 (range 1-7) megavoltage and 1.4 (range 0-4) orthovoltage units were available per institution; 32 institutions (24%) had no orthovoltage equipment. A mean of 20,082 patients were treated annually: 456 (2%) for inflammatory diseases (221 hidradenitis, 78 local infection, 23 parotitis; 134 not specified) 12,600 (63%) for degenerative diseases (2711 peritendinitis humeroscapularis, 1555 epicondylitis humeri; 1382 plantar/dorsal heel spur; 2434 degenerative osteoarthritis; 4518 not specified); 927 (5%) for hyperproliferative diseases (146 Dupuytren's contracture, 382 keloids; 155 Peyronie's disease; 244 not specified); 1210 (6%) for functional disorders (853 Graves' orbitopathy; 357 not specified); and 4889 (24%) for other disorders (e.g., 3680 heterotopic ossification prophylaxis). In univariate analysis, there were geographic (West vs. East Germany) differences in using radiation therapy (RT) for inflammatory and degenerative disorders, and institutional differences (university versus community hospitals) in using RT for hyperproliferative and functional disorders (p < 0.05). The prescribed dose concepts were mostly in the low dose range, <10 Gy but varied widely and inconsistently within geographic regions and institutions. CONCLUSION: Radiation therapy is a well-accepted and frequently practiced treatment for several benign diseases in Germany; however, there are significant geographic and institutional differences. As the number of orthovoltage units decreases, an increasing patient load will demand more megavoltage units, which may compromise the cost-effectiveness of this treatment. Only 4% of all clinical institutions have been involved in controlled clinical trials. To maintain a high level of RT service to other disciplines, RT treatment guidelines, quality control, and continuing medical education are required.

Disease Management↗
PubMed2000

Engineering of a proteolytically stable human beta 2-adrenergic receptor/maltose-binding protein fusion and production of the chimeric protein in Escherichia coli and baculovirus-infected insect cells.

The hydrophobic human beta 2 adrenergic receptor was produced in fusion to the hydrophilic maltose-binding protein (MalE) in Escherichia coli. Photoaffinity labeling with the adrenergic ligand [125I]cyanopindolole-diazirine indicated that the majority of the protein was proteolyzed in the intergenic region between the fusion partners after production in E. coli. The simple and fast genetics of the bacterium enabled us to engineer a linker with an increased proteolytic stability. The fusion protein produced in E. coli was fully functional with respect to binding of adrenergic ligands and coupling to stimulatory GTP-binding protein. The production level with 3 pmol receptor fusion protein per mg membrane protein in a crude membrane preparation was significantly higher than those reported for other beta 2 adrenergic receptor constructs in E. coli. After solubilization with dodecanoyl sucrose, the fusion protein was purified to near homogeneity by affinity chromatography on immobilized Ni2+ ions (binding to a C-terminal His6-tag) and on crosslinked amylose (binding to the MalE). In order to achieve higher production levels, the fusion protein preceded by an insect signal peptide was produced in baculovirus-infected insect cells. As expected, the production level with about 17 pmol receptor per mg membrane protein was higher in the insect cells than in E. coli. The receptor fusion protein produced in the insect cells bound adrenergic ligands and activated heterotrimeric GTP-binding proteins with biochemical properties comparable to that of the unfused receptor.

ATP-Binding Cassette Transporters↗
PubMed2000

[Radiotherapy of lymphatic fistula and lymphocele].

BACKGROUND: The treatment of persistent postoperative lymphatic fistulas or lymphoceles is often a problem. Approximately 2% of patients will develop lymphatic fistula after vascular surgery. This can require a long lasting conservative therapy. If spontaneous cure fails, a second operation with wound revision becomes necessary. We studied low-dose percutaneous radiotherapy to be used as an alternative treatment in addition to conservative or surgical therapy. PATIENTS AND METHODS: Between 1989 and 1998 29 patients (25 with lymphatic fistulas, 4 with lymphoceles) received radiation therapy. Depending on the depth of the fistula 27 patients were treated with electrons (7 to 18 MeV). Two other patients suffering of retroperitoneal lymphoceles received a treatment with photons (15 MV). In all patients the fractionation was 4- to 5 x 1.0 Gy/week and the dose ranged from 3 to 12 Gy depending upon the onset of the radiation therapy effect. RESULTS: In 27 of 28 evaluable patients a complete disappearance of the fistula or lymphocele was achieved by radiation during therapy or shortly afterwards. In 1 case no benefit was observed after a dose of 11 Gy. This patient required further surgery with wound exploration. CONCLUSION: Low dose percutaneous radiotherapy (up to 10 to 12 Gy) is effective to heal lymphatic fistulas and lymphoceles without complications. Individual dosage is required because doses even lower than 10 Gy may be effective. Radiation can be effective even after a failed conservative therapy or instead of surgery.

Adult↗
PubMed2000

Preliminary report: Dynamic stereopsis in patients with impaired binocular function.

In this study, 46 strabismic patients aged between 9 and 58 years were tested for dynamic stereopsis in the peripheral visual field with up to 20 degrees eccentricity. Squint angles ranged from +30 to -36 degrees. The effect of surgical realignment of the visual axes on dynamic stereopsis was tested before and after surgery in 40 of these patients. Of the 46 patients, 23 had esotropia and 23 exotropia. A test device was used which presented two projected squares in polarized light (each square being perceived monocularly through a polarization filter) in horizontal motion, thus creating a three-dimensional impression. Patients were tested qualitatively for dynamically stereoactive fields of vision and quantitatively for the threshold value needed to create a three-dimensional impression. We found residual dynamic stereopsis in 30% of patients who had no central static stereopsis. 56% of the patients improved after surgery, either through a significant (p < 0.01) gain of stereoactive fields or through a decrease in threshold values. This emphasizes the necessity of creating a test device suitable for everyday clinical use. Strabismus surgery is especially beneficial in connection with traffic and sports medicine, regardless of the effect on classical tests.

Adolescent↗