Isothermal furnace for long-term in situ and real-time X-radiography solidification experiments.

A new x-ray isothermal furnace has been developed, suitable for in situ observations of semi-solid processes including the transition from dendritic to globulitic grain morphology and grain coarsening in metallic samples. A homogeneous, isothermal temperature field is achieved using a novel heater concept. The furnace structure is sandwich-like with heating elements positioned in the beam line and parallel to the sample. Planar heat transfer to the sample enables measurements with low cooling rates and a minimized temperature gradient. Cooling rates from 0.1 to 15 K min-1 can be controlled in the temperature range 1170-670 K. The furnace setup is integrable in the existing rotatable laboratory x-ray facility (X-RISE) at the German Aerospace Center (DLR). In this setup, an effective pixel size of 3 µm and a field of view of 8 mm in diameter can be achieved. Preliminary solidification and semi-solid experiments in the hypo-eutectic alloy systems Al-Ge and Al-Cu, inoculated with Al-5Ti-1B grain refiner, are presented. They indicate a very uniform temperature distribution in the sample.

[An unusually painful leg ulcer in an 81-year-old patient: an interdisciplinary challenge]. / Außergewöhnlich schmerzhaftes Ulcus cruris bei einem 81­jährigen Patienten ­ eine interdisziplinäre Herausforderung.

An 81-year-old male patient with a history of peripheral arterial disease (PAD) was admitted to the authors' outpatient clinic with a painful lower leg ulcer. As the degree of PAD did not correspond to the clinical findings, multiple biopsies were taken from the base and edge of the ulcer. This resulted in the histopathological and clinical diagnosis of pyoderma gangrenosum (PG). Since PG is often associated with numerous underlying diseases, further thorough examinations were performed. A mass in the gastric antrum suspicious for malignancy was histopathologically identified as gastric cancer (signet ring cell carcinoma). The PG was successfully treated with cortisone p.o. and tacrolimus ointment. Since the cancer was locally limited, the patient underwent surgery involving gastric resection with D2 lymphadenectomy and gastrojejunostomy (Roux-en­Y anastomosis).

XRISE-M: X-radiography facility for solidification and diffusion studies of alloys aboard sounding rockets.

A compact fully protected microfocus X-radiography facility (XRISE-M) is presented for the study of microstructure evolution during the solidification of thin liquid alloy samples and chemical diffusion in liquid binary alloys in situ and in real-time aboard a sounding rocket. XRISE-M presently enables the simultaneous processing of either two near-isothermal solidification furnaces or a combination of a linear-shear cell diffusion furnace and a near-isothermal solidification furnace. For optimal detector calibration shortly before flight, the furnaces can be rotated around the central beam axis and calibration images can be recorded. The facility allows preheating the samples into the liquid state prior to lift-off without leakage during the ascent phase at accelerations of up to 27 g. Macrosegregation on remelting of thin metal samples for microstructure evolution investigations is prevented by an inclinable furnace metric. The use of ion-getter pumps for vacuum generation enables us to exploit the entire available time of reduced gravity for image recording and data acquisition. With the device and currently available sample environments, microstructure formation upon solidification and chemical diffusion under purely diffusive conditions in alloys can be investigated. The facility can be used equally for other investigations such as granular matter dynamics or metal foaming, provided that suitable experiment inserts are developed in the future.

New Twists of 3D Chiral Metamaterials.

Rationally designed artificial materials, called metamaterials, allow for tailoring effective material properties beyond ("meta") the properties of their bulk ingredient materials. This statement is especially true for chiral metamaterials, as unlocking certain degrees of freedom necessarily requires broken centrosymmetry. While the field of chiral electromagnetic/optical metamaterials has become rather mature, the field of elastic/mechanical metamaterials is just emerging and wide open. This research news reviews recent theoretical and experimental progress concerning 3D chiral mechanical and optical metamaterials, with special emphasis on work performed at KIT.

Implementation of a miniaturised navigation system in head and neck surgery for the detection and removal of foreign bodies.

The removal of embedded blast-generated fragments from soft tissue is very difficult, especially in the head and neck regions. First, because many retained foreign materials are non-metallic and can, therefore, not be detected by fluoroscopy, and second, because a broad exploration of the soft tissue is not possible in the facial area for functional and cosmetic reasons. Intraoperative navigation computer-assisted surgery (CAS) may facilitate the retrieval of foreign bodies and reduce exploration trauma. In a blind trial, five test specimens of different materials (glass, metal, wood, plastic, and stone) were inserted on the left and right sides of the head and neck of ten body donors through an intraoral incision. A second physician then detected and removed the foreign bodies from one side of the body without and from the other side of the body with navigation. We measured the duration of surgery, the extent of tissue trauma caused during surgery, the time it took to remove the foreign bodies, and the subjective evaluation of the usefulness of navigation. With the aid of the navigation system, the various foreign bodies were detected after an average of 26.7 (±35.1) s (p < 0.0001) and removed after an average of 79.1 (±66.2) s (p = 0.0239), with an average incision length of 10.0 (±3.5) mm. Without the navigation system, the foreign bodies were located after an average of 86.5 (±77.7) s and removed after an average of 74.1 (±45.9) s, with an average incision length of 13.0 mm (±3.6) mm (=0.0007). Intraoperative navigation systems are a valuable tool for removing foreign bodies from the soft tissue of the face and neck. Both the duration of surgery and the incision length can be reduced using navigation systems. Depending on the material of the foreign bodies and the signal intensity in the CT/MRI scanner, however, the detection reliability varies. All in all, navigation is considered to be a useful tool.

Wiring up pre-characterized single-photon emitters by laser lithography.

Future quantum optical chips will likely be hybrid in nature and include many single-photon emitters, waveguides, filters, as well as single-photon detectors. Here, we introduce a scalable optical localization-selection-lithography procedure for wiring up a large number of single-photon emitters via polymeric photonic wire bonds in three dimensions. First, we localize and characterize nitrogen vacancies in nanodiamonds inside a solid photoresist exhibiting low background fluorescence. Next, without intermediate steps and using the same optical instrument, we perform aligned three-dimensional laser lithography. As a proof of concept, we design, fabricate, and characterize three-dimensional functional waveguide elements on an optical chip. Each element consists of one single-photon emitter centered in a crossed-arc waveguide configuration, allowing for integrated optical excitation and efficient background suppression at the same time.

The course of headache in idiopathic intracranial hypertension: a 12-month prospective follow-up study.

BACKGROUND AND PURPOSE: Our aim was to prospectively describe the course of headache during the first year of idiopathic intracranial hypertension (IIH). METHODS: Patients with newly diagnosed IIH were consecutively included from December 2010 to June 2013. Treatment according to standard guidelines was initiated. Headache history was obtained by headache diaries and standardized interviews performed at baseline and after 1, 2, 3 and 12 months. Parallel changes in papilledema were assessed by optical coherence tomography (OCT). All patients had comprehensive neuro-ophthalmological examinations including automated perimetry. RESULTS: Forty-four patients were included. Thirty-five patients completed the 12-month follow-up. Dramatic improvement in headache occurred within the first weeks after diagnosis. After 1 year, 15 patients reported no or only infrequent headache. However, 15 of the remaining 20 patients reported sustained chronic headache. Early age of onset and high diagnostic intracranial pressure (ICP) were associated with better headache outcome (≤1 headache days/month) after a year. Papilledema decreased rapidly within the first 2 months of diagnosis. After 1 year, OCT measures had normalized. Visual outcome was excellent in most patients. CONCLUSIONS: Although headache in 43% of patients responded well to ICP management, sustained long-term headache was seen in the remaining patients, despite resolution of papilledema. Headache in IIH may thus be attributed to more complex mechanisms than ICP elevation alone. High ICP and young age were associated with better headache outcome. Early treatment according to standard guidelines seems sufficient to ensure excellent visual outcome in the vast majority of patients.

An elasto-mechanical unfeelability cloak made of pentamode metamaterials.

Metamaterial-based cloaks make objects different from their surrounding appear just like their surrounding. To date, cloaking has been demonstrated experimentally in many fields of research, including electrodynamics at microwave frequencies, optics, static electric conduction, acoustics, fluid dynamics, thermodynamics and quasi two-dimensional solid mechanics. However, cloaking in the seemingly simple case of three-dimensional solid mechanics is more demanding. Here, inspired by invisible core-shell nanoparticles in optics, we design an approximate elasto-mechanical core-shell 'unfeelability' cloak based on pentamode metamaterials. The resulting three-dimensional polymer microstructures with macroscopic overall volume are fabricated by rapid dip-in direct laser writing optical lithography. We quasi-statically deform cloak and control samples in the linear regime and map the displacement fields by autocorrelation-based analysis of recorded movies. The measured and the calculated displacement fields show very good cloaking performance. This means that one can elastically hide objects along these lines.

Collective effects in second-harmonic generation from split-ring-resonator arrays.

Optical experiments on second-harmonic generation from split-ring-resonator square arrays show a nonmonotonic dependence of the conversion efficiency on the lattice constant. This finding is interpreted in terms of a competition between dilution effects and linewidth or near-field changes due to interactions among the individual elements in the array.

Waveguides in three-dimensional photonic-bandgap materials by direct laser writing and silicon double inversion.

Three-dimensional complete photonic-bandgap materials offer unique opportunities regarding the integration of optical waveguide architectures in three dimensions. However, corresponding experimental realizations are truly sparse. Here, we fabricate such waveguides using direct laser writing and a silicon double-inversion procedure. The optical characterization is in good agreement with theoretical calculations, raising hopes that even more complex architectures may soon come into reach.

Twisted split-ring-resonator photonic metamaterial with huge optical activity.

Coupled split-ring-resonator metamaterials have previously been shown to exhibit large coupling effects, which are a prerequisite for obtaining large effective optical activity. By a suitable lateral arrangement of these building blocks, we completely eliminate linear birefringence and obtain pure optical activity and connected circular optical dichroism. Experiments around a 100 THz frequency and corresponding modeling are in good agreement. Rotation angles of about 30 degrees for 205 nm sample thickness are derived.

Fabrication and characterization of silicon woodpile photonic crystals with a complete bandgap at telecom wavelengths.

By using direct laser writing into a novel commercially available photoresist and a silicon-double-inversion procedure followed by tempering of the silicon structures, we realize high-quality centered-tetragonal woodpile photonic crystals with complete photonic bandgaps near 1.55 microm wavelength. The 6.9% gap-to-midgap ratio bandgap is evidenced by the comparison of measured transmittance and reflectance spectra with band-structure and scattering-matrix calculations.

Three-dimensional chiral photonic superlattices.

We investigate three-dimensional photonic superlattices composed of polymeric helices in various spatial checkerboard-like arrangements. Depending on the relative phase shift and handedness of the chiral building blocks, different circular-dichroism resonances appear or are suppressed. Samples corresponding to four different configurations are fabricated by direct laser writing. The measured optical transmittance spectra are in good agreement with numerical calculations.

[Optic disc drusen or true papilledema?]. / Drusen de la tête du nerf optique ou oedème papillaire?

INTRODUCTION: Bilateral optic disc drusen can mimic papilledema, raising the question of intracranial hypertension and sometimes prompting unnecessary or invasive procedures. STATE OF THE ART AND PERSPECTIVES: Optic disc drusen are benign calcified masses, often visible within the optic nerve head. However, their clinical diagnosis can be more difficult at earlier stages of life, when they are buried within the optic nerve. Visual field loss can occur in patients with longstanding optic disc drusen. CONCLUSION: Ophthalmoscopy and B-scan ocular ultrasonography allow appropriate diagnosis of bilateral optic disc drusen mimicking papilledema. On rare occasions, optic disc drusen can be associated with ischemic complications, the other causes of drusen-related visual loss being exceptionally rare.

Strong optical activity from twisted-cross photonic metamaterials.

Following a recent theoretical suggestion and microwave experiments, we fabricate photonic metamaterials composed of pairs of twisted gold crosses using two successive electron-beam-lithography steps and intermediate planarization via a spin-on dielectric. The resulting two effective resonances of the coupled system lie in the 1-2 microm wavelength regime and exhibit pronounced circular dichroism, while the circular polarization conversion is very small. In between the two resonances, we find a fairly broad spectral regime with strong optical activity, i.e., with a pure rotation of incident linear polarization. The measured optical transmittance spectra agree well with theory.

Second-harmonic generation from split-ring resonators on a GaAs substrate.

We study second-harmonic generation from gold split-ring resonators on a crystalline GaAs substrate. By systematically varying the relative orientation of the split-ring resonators with respect to the incident linear polarization of light and the GaAs crystallographic axes, we unambiguously identify a nonlinear contribution that originates specifically from the interplay of the local fields of the split-ring resonators and the bulk GaAs second-order nonlinear-susceptibility tensor. The experimental results are in good agreement with theoretical modeling.

One dimensional resonant Fibonacci quasicrystals: noncanonical linear and canonical nonlinear effects.

A detailed experimental and theoretical study of the linear and nonlinear optical properties of different Fibonacci-spaced multiple-quantum-well structures is presented. Systematic numerical studies are performed for different average spacing and geometrical arrangement of the quantum wells. Measurements of the linear and nonlinear (carrier density dependent) reflectivity are shown to be in good agreement with the computational results. As the pump pulse energy increases, the excitation-induced dephasing broadens the exciton resonances resulting in a disappearance of sharp features and reduction in peak reflectivity.

Attempts to grow optically coupled Fibonacci-spaced InGaAs/GaAs quantum wells result in surface gratings.

An instability in the growth of nonperiodic InGaAs/GaAs multiple quantum well samples, ordinarily of high-quality when grown with equal periods of order of half the wavelength of light in the material, leads to a dramatic microscopic, self-organized surface grating. This effect was discovered while growing quantum wells with two unequal barrier lengths arranged in a Fibonacci sequence to form an optical quasicrystal. A laser beam incident normal to the surface of the sample is diffracted into a propeller-shaped pattern. The sample surface has a distinctly cloudy appearance when viewed along one crystal axis but is mirror-like when the sample is rotated 90 degrees. The instability results in a five-fold increase in the absorption linewidth of the heavy-hole exciton transition. Atomic force microscopy, transmission electron microscopy, and scanning electron microscopy were used to study the samples.

Excitonic polaritons in Fibonacci quasicrystals.

The fabrication and characterization of light-emitting one-dimensional photonic quasicrystals based on excitonic resonances is reported. The structures consist of high-quality GaAs/AlGaAs quantum wells grown by molecular-beam epitaxy with wavelength-scale spacings satisfying a Fibonacci sequence. The polaritonic (resonant light-matter coupling) effects and light emission originate from the quantum well excitonic resonances. Measured reflectivity spectra as a function of detuning between emission and Bragg wavelength are in good agreement with excitonic polariton theory. Photoluminescence experiments show that active photonic quasicrystals, unlike photonic crystals, can be good light emitters: While their long-range order results in a stopband similar to that of photonic crystals, the lack of periodicity results in strong emission.