Biomedical subjects
Publications and source records attributed to M Wegener.
We further miniaturize a recently established silver-based negative-index metamaterial design. By comparing transmittance, reflectance, and phase-sensitive time-of-flight experiments with theory, we infer a real part of the refractive index of -0.6 at a 780 nm wavelength--which is visible in the laboratory.
We fabricate and characterize one-dimensional magnetic (rather than dielectric) photonic crystals for the first time. Our model system is a one-dimensional periodic lattice of gold-wire pairs. Each pair can be viewed as a magnetic coil with two slits and represents a "magnetic atom." Strong coupling between the resulting magnetic-dipole resonance and the Bragg resonance is accomplished by an adjacent dielectric slab waveguide, giving rise to an avoided crossing at near-infrared wavelengths. Our experimental findings are in excellent agreement with theory.
We present magnetic metamaterials composed of 35 nm minimum feature-size gold split-ring resonators with a fundamental magnetic resonance at a wavelength of 900 nm. Corresponding calculations reveal excellent agreement with the experiments and show that the limits of size scaling have been reached.
Using direct laser writing, we fabricate photoresist templates for 3D-2D-3D photonic crystal heterostructures for what we believe to be the first time. The optical properties of these structures are directly compared with the theoretical ideal, revealing good agreement and hence good sample quality. This provides an experimental starting point for the microfabrication and testing of broadband, 3D air-waveguide microcircuitry in photonic bandgap materials.
We study the optical properties of metamaterials made from cut-wire pairs or plate pairs. We obtain a more pronounced optical response for arrays of plate pairs, a geometry that also eliminates the undesirable polarization anisotropy of the cut-wire pairs. The measured optical spectra agree with simulations, revealing negative magnetic permeability in the range of telecommunications wavelengths. Thus nanoscopic plate pairs might serve as an alternative to the established split-ring resonator design.
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.
The carrier-envelope phase of a laser pulse has recently become an important quantity in extreme nonlinear optics. Because of the topological Gouy phase, it changes while the pulse propagates through the focus of a lens. This variation is measured by a simple solid-state-based approach. The experimental results are analyzed by comparison with simple analytical model calculations.
Overall, vertebroplasty has a low complication rate. Nevertheless, severe complications can occur. The majority of these are related to cement extrusion. The rate of cement leakage is often obtained by X-ray, with only a single leak registration per vertebra. Detection rate of leaks in comparison with CT and inter-observer reliability for X-ray is, in large parts, unknown. We conducted this study to determine the value of fluoroscopy and X-ray used to detect cement leakage as compared to CT scans. Intraoperative findings in lateral fluoroscopy by the surgeon, and postoperative findings in X-rays by two orthopaedic surgeons, were compared with CT scans for the same study group. Multiple cement leakage was considered, and agreement rate was determined. The detection rate for leaks was 34% for lateral X-ray and 48% for lateral and AP view. Additional AP views only enhanced the detection of leaks in the segmental veins. The agreement rate between fluoroscopy/X-ray and CT scans ranged between 66% and 74%, while inter-observer reliability showed only fair agreement. The rate of cement leaks in vertebroplasty is high if multiple leaks are considered in CT scans. Detection rates using X-rays are low and complicated by only fair inter-observer agreement. Leaks in the basivertebral veins are frequently misinterpreted and can lead to severe complications. Therefore, CT scans should be obtained to calculate the exact leakage rate and to assess persistent or new pain occurring postoperatively.
We observe a triplet around the third harmonic of the semiconductor band gap when exciting 50-100 nm thin GaAs films with 5 fs pulses at 3 x 10(12) W/cm(2). The comparison with solutions of the semiconductor Bloch equations allows us to interpret the observed peak structure as being due to a two-band Mollow triplet. This triplet in the optical spectrum is a result of light-induced gaps in the band structure, which arise from coherent band mixing. The theory is formulated for full tight-binding bands and uses no rotating-wave approximation.
In contrast with traditional nonlinear optics, a peak at the spectral position of the second harmonic of a laser can also be generated in an inversion-symmetric medium in the regime of extreme nonlinear optics. We describe the underlying mechanism of such third-harmonic generation in disguise of second-harmonic generation and compare theory with the optical as well as the radio-frequency spectra measured in recent experiments on thin ZnO films. The peak at twice the carrier-envelope offset frequency in the radio-frequency spectra is shown to be an unambiguous signature of such a process.
We study the influence of the carrier-envelope offset phase of few-cycle pulses on nonperturbative resonant extreme nonlinear optics in a semiconductor. If the Rabi frequency becomes comparable to the light frequency, the different Rabi sidebands interfere around twice the laser center frequency, giving rise to a signal which strongly depends on the carrier-envelope offset phase. This signature should be measurable in GaAs samples.
Excessive ineffective erythropoiesis in thalassemia intermedia may cause paravertebral pseudotumors of extramedullary hematopoiesis. Due to the proximity to the spinal canal, these paravertebral masses carry the risk of severe neurological damage. Treatment strategies include hypertransfusion, radiotherapy, and laminectomy. Hydroxyurea, stimulating fetal hemoglobin synthesis, may represent an alternative therapeutic approach. We report on a 26-year-old patient suffering from thalassemia intermedia with progressive anemia symptoms and presenting multiple intrathoracic paravertebral pseudotumors of extramedullary hematopoiesis. Hypertransfusion therapy and splenectomy were followed by regular transfusion (baseline hemoglobin 10 g/dl) and chelation with desferrioxamine. With this treatment, clinical symptoms disappeared, paravertebral hematopoietic masses did not progress, but severe hemosiderosis developed within a few years. Hydroxyurea therapy was initiated to increase the efficacy of erythropoiesis, thereby reducing the required transfusion volume but suppressing concomitantly further expansion of extramedullary hematopoiesis, and finally leading to a reduction of transfusional iron load. Treatment was started with 4 mg/kg per day and stepwise increased to 12.5 mg/kg per day. The fetal hemoglobin concentration increased from 4.5 to 5.5 g/dl after 1 year and to 9.9 g/dl after 2 years of treatment. The yearly transfusion volume was halved during the 1st year of treatment. At present, after 26 months of treatment, the patient has been transfusion-independent for 10 months. Serum ferritin levels decreased from 2844 to 1335 ng/ml. Size and shape of paravertebral hematopoietic pseudotumors remained stable. No side effects of hydroxyurea have been observed. In thalassemia intermedia patients with extramedullary hematopoiesis, hydroxyurea may lead to independence from regular transfusion therapy without further expansion of ectopic hematopoietic tissue.
CASE HISTORY AND DIAGNOSIS: A 20-year-old African man was admitted to hospital with anemia, eosinophilia, raised liver enzymes and hepatosplenomegaly. Previously, on arrival in Germany, he had undergone a routine medical check-up where simple microscopy of a feces sample as well as serology for lues, AIDS and hepatitis B had all been negative. In our hospital a stool specimen was examined for ova and parasites and revealed ova of Schistosoma mansoni and confirmed the diagnosis of bilharziosis. For the detection of helmintic ova repeated stool examinations with use of concentration techniques are required. Staging by endoscopies, ultrasonography revealed colon pseudopolyposis and periportal fibrosis complicated by portal hypertension and esophageal varices. TREATMENT AND COURSE: Chemotherapy with Praziquantel was effective in eliminating the parasites but in advanced stages chronic fibrotic changes are usually irreversible. Further monitoring will therefore be necessary in our patient. CONCLUSION: Due to increasing migration and international travel, also doctors working in industrialized countries should be aware of tropical diseases.
For excitation of the model semiconductor GaAs with optical pulses which are both extremely short ( 5 fs) and extremely intense ( approximately 10(12) W cm(-2)), we can meet the condition that the Rabi frequency becomes comparable to the band gap frequency-a highly unusual and previously inaccessible situation. Specifically, in this regime, we observe carrier-wave Rabi flopping, a novel effect of nonlinear optics which has been predicted theoretically and which is related to the failure of the area theorem.
Autocorrelation spectroscopy on the basis of thousands of individual near-field photoluminescence spectra of single ultrathin CdSe layers at low temperatures exhibits a strong positive correlation peak around 18 meV energy with a width of 5 meV. Using simulations and experiments as a function of temperature and laser intensity, we can exclude interpretations along the lines of biexcitons or phonon sidebands. We attribute this feature to the splitting of ground state and an excited state in individual quantum islands. This interpretation implies that the potential minima are rather uniform in size and that the distribution of excitons is nonthermal.
PURPOSE: To examine the incidence of intraprosthetic thrombotic deposits in aortic endografts. METHODS: Transfemoral implantation of tube or bifurcated stent-grafts was performed in 82 patients (75 men; average age 67.7 years, range 25-88) for treatment of aneurysms of the abdominal (n = 73) or thoracic (n = 9) aorta in a 3.5-year period. Patients underwent 3-phase helical computed tomographic (CT) examinations at 3-month intervals. The length and cross-sectional area of any thrombotic deposits were measured from axial and 3-dimensional CT images. RESULTS: Over a 12.1-month mean follow-up, intraluminal deposits of thrombotic material were observed in 19 (23.2%) patients, all with infrarenal endografts that were predominately of a bifurcated design. The first signs of thrombus formation occurred on average 7 months postoperatively (range 1 week to 20 months). In 16 patients, nonocclusive deposits of thrombotic material were seen in the aortic segment of the endograft; a graft limb was involved in 5 patients. Three graft limbs occluded owing to kinking; no thrombus was seen on CT scans taken prior to occlusion. In 3 cases the thrombotic deposits disappeared completely from the prosthesis lumen during follow-up. CONCLUSIONS: Based on this small experience, nearly 1 in 5 patients may experience some degree of intraluminal thrombus following endovascular treatment of aortic aneurysms. Whether the deposition of thrombus is influenced by the geometry of the aortic stent-graft or by flow conditions within the prosthetic lumen must be determined in future studies.
We predict a carrier-density dependent oscillation, which is superimposed on the decay of the coherent control photon echo signal of a semiconductor. It reflects the oscillatory transfer of excitation back and forth between electrons and a mixed plasmon-phonon mode. This signature provides obvious and unique evidence for the finite duration of the interaction process, i.e., evidence for the collective Coulomb quantum kinetics. The theoretical predictions for the model semiconductor GaAs are reproduced in corresponding experiments.
BACKGROUND: Laparoscopic ultrasound is an alternative to operative cholangiogram for evaluation of the common bile duct (CBD) during laparoscopic cholecystectomy. It is a safe, fast, and reliable method for detecting choledocholithiasis. METHODS: We prospectively evaluated the sensitivity and specificity of laparoscopic ultrasound (LUS) and digital fluorocholangiogram (DFCG) in a three-phase study of 360 consecutive patients. RESULTS: In phase I, 140 patients undergoing laparoscopic cholecystectomy had LUS performed first, followed by DFCG. Thirteen patients had CBD calculi identified on LUS. Four patients with confirmed (two cases) or presumed (two cases) CBD calculi on DFCG were not identified on LUS. Thus, the specificity of LUS was 100%, whereas the sensitivity was 76.5%. DFCG had four false positives, for a sensitivity of 100% with a specificity of 96.7%. LUS was performed, on average, in 6.6 min, whereas DFCG required 10.9 min to perform. In phase II, the infusion of saline through a cystic duct catheter was performed in instances where the distal CBD could not be well seen. This maneuver distended the intrapancreatic portion of the CBD, allowing better visualization. Nine stones were identified on LUS in 78 patients, increasing the sensitivity to 100%. One false positive DCFG was encountered, resulting in a sensitivity of 100% and a specificity of 98.6%. In phase III, we performed routine LUS and used DFCG only in select cases. The sensitivity and specificity for LUS were 95.7% and 100%, respectively, whereas DFCG had a sensitivity of 95.2% and a specificity of 100%. One patient in phase III has returned 11 months post-op with a CBD stone. This was initially missed on LUS, DFCG, and postoperative ERCP. The sensitivity and specificity in all 360 patients were 90% and 100% for LUS and 98.1% and 98.1% for DFCG, respectively. A total of five CBD stones were missed by LUS, four early in the study (phase I). One missed on LUS in phase III was also missed by DFCG and ERCP. CONCLUSIONS: LUS is a reliable alternative to DFCG during laparoscopic cholecystectomy (LC). With experience, it is as sensitive as DFCG and more specific. It is more rapidly performed than cholangiography.