Single-particle and collective excitations of polar water molecules confined in nano-pores within a cordierite crystal lattice.

Recently, the low-temperature phase of water molecules confined within nanocages formed by the crystalline lattice of water-containing cordierite crystals has been reported to comprise domains with ferroelectrically ordered dipoles within the a, b-planes which are antiferroelectrically alternating along the c-axis. In the present work, comprehensive broad-band dielectric spectroscopy is combined with specific heat studies and molecular dynamics and Monte Carlo simulations in order to investigate in more detail the collective modes and single-particle excitations of nanoconfined water molecules. From DFT-MD simulations we reconstruct the potential-energy landscape experienced by the H2O molecules. A rich set of anisotropic temperature-dependent excitations is observed in the terahertz frequency range. Their origin is associated with the complex rotational/translational vibrations of confined H2O molecules. A strongly temperature dependent relaxational excitation, observed at radio-microwave frequencies for the electric field parallel to the crystallographic a-axis, E||a is analyzed in detail. The temperature dependences of loss-peak frequency and dielectric strength of the excitation together with specific heat data confirm a ferroelectric order-disorder phase transition at T0 ≈ 3 K in the network of H2O dipoles. Additional dielectric data are also provided for polarization E||b, too. Overall, these combined experimental investigations enable detailed conclusions concerning the dynamics of the confined water molecules that develop within their microscopic energy landscapes.

La2Pd2In: superconductivity and lattice properties at ambient and elevated pressures.

Lattice and electronic properties of La2Pd2In were studied at ambient and elevated pressures so as to determine features related to a specific atomic coordination without any influence of magnetism. We describe temperature dependences of lattice parameters, heat capacity and electrical resistivity of single-crystalline La2Pd2In (s.g.P4/mbm) in a broad temperature range 0.09-300 K. Together with the anisotropic effect of hydrostatic pressure, showing that the lattice is more compressible in the basal plane, we can conclude that the lattice is affected by degrees of freedom of the La atoms with positions not imposed by symmetry. The lattice anisotropy is smaller than that found for isostructural ferromagnet Ce2Pd2In. The equilibrium bulk modulusB0= (48 ± 3) GPa was determined on the basis of individual linear compressibilities. Measurement of electrical resistivity indicated a superconducting state belowT= 0.59 K with a low critical field 0.005 T atT= 380 mK. The onset of superconducting state as a bulk property of La2Pd2In was confirmed by measurements of specific heat and AC magnetic susceptibility. Experimental data can be accounted by first-principles electronic-structure calculations based on density-functional theory. The measured Sommerfeld coefficientγ= 10.6 mJ mol-1 K-2, only marginally exceeding the calculatedγ= 9.34 mJ mol-1 K-2, indicates only weak electronic correlations.

Impact of isoelectronic substitution and hydrostatic pressure on the quantum critical properties of CeRhSi3.

There is an ongoing dispute in the community about the absence of a magnetic quantum critical point (QCP) in the noncentrosymmetric heavy fermion compound CeRhSi3. In order to explore this question we prepared single crystals of CeRh(Si1-x Ge x )3 with x = 0.05 and 0.15 and determined the temperature-pressure (T-p) phase diagram by means of measurements of the electrical resistivity. The substitution of isoelectronic but large Ge enforces a lattice volume increase resulting in a weakening of the Kondo interaction. As a result, the x = 0.05 and x = 0.15 compound exhibit a transition into the antiferromagnetic (AFM) at higher temperatures being T N = 4.7 K and T N1 = 19.7 K, respectively. Application of pressure suppresses T N (T N1) monotonically and pressure induced superconductivity is observed in both Ge-substituted compounds above p ⩾ 2.16 GPa (x = 0.05) and p ⩾ 2.93 GPa (x = 0.15). Extrapolation of T N(p) → 0 of CeRh(Si0.95Ge0.05)3 yields a critical pressure of p c ≈ 3.4 GPa (in CeRh(Si0.85Ge0.15)3 p c ≈ 3.5 GPa) pointing to the presence of an AFM QCP located deep inside the superconducting state.

Dielectric ordering of water molecules arranged in a dipolar lattice.

Intermolecular hydrogen bonds impede long-range (anti-)ferroelectric order of water. We confine H2O molecules in nanosized cages formed by ions of a dielectric crystal. Arranging them in channels at a distance of ~5 Å with an interchannel separation of ~10 Å prevents the formation of hydrogen networks while electric dipole-dipole interactions remain effective. Here, we present measurements of the temperature-dependent dielectric permittivity, pyrocurrent, electric polarization and specific heat that indicate an order-disorder ferroelectric phase transition at T0 ≈ 3 K in the water dipolar lattice. Ab initio molecular dynamics and classical Monte Carlo simulations reveal that at low temperatures the water molecules form ferroelectric domains in the ab-plane that order antiferroelectrically along the channel direction. This way we achieve the long-standing goal of arranging water molecules in polar order. This is not only of high relevance in various natural systems but might open an avenue towards future applications in biocompatible nanoelectronics.

How reliable are the risk estimates for X-ray examinations in forensic age estimations? A safety update.

Possible biological side effects of exposure to X-rays are stochastic effects such as carcinogenesis and genetic alterations. In recent years, a number of new studies have been published about the special cancer risk that children may suffer from diagnostic X-rays. Children and adolescents who constitute many of the probands in forensic age-estimation proceedings are considerably more sensitive to the carcinogenic risks of ionizing radiation than adults. Established doses for X-ray examinations in forensic age estimations vary from less than 0.1 microSv (left hand X-ray) up to more than 800 microSv (computed tomography). Computed tomography in children, as a relatively high-dose procedure, is of particular interest because the doses involved are near to the lower limit of the doses observed and analyzed in A-bombing survivor studies. From these studies, direct epidemiological data exist concerning the lifetime cancer risk. Since there is no medical indication for forensic age examinations, it should be stressed that only safe methods are generally acceptable. This paper reviews current knowledge on cancer risks associated with diagnostic radiation and aims to help forensic experts, dentists, and pediatricians evaluate the risk from radiation when using X-rays in age-estimation procedures.

Radiofrequency ablation of experimental bone metastases in nude rats.

PURPOSE: Animal models are indispensable to investigate bone metastasis and to test different preclinical therapy options. Radiofrequency ablation is an upcoming technique for palliating pain from bone metastases. The aim of this study was to generate osteolytic lesions and to enable a technique to achieve access to the bone to successfully carry out radiofrequency ablation. MATERIALS AND METHODS: Human breast cancer cell line MDA-MB-231 (10(5) tumor cells) was implanted into the femur of 10 nude rats using a drill hole after arthrotomy of the knee joint and opening of the femur through the notch. Weekly CT- and MRI-scans were performed to document number and size of bone metastases. Radiofrequency ablation (22G bipolar and impedance-controlled RF-applicator, 2-4 Watt, 3 min application time) was carried out. One week after RFA, the animals were sacrificed and macroscopic and histological examination followed. For statistical analysis, paired comparison procedures were used. RESULTS: Inoculation of the tumor cells was well tolerated. The mean time of the surgical procedure was 6 minutes. All animals developped local bone metastases. Mean time to metastasis was 8 weeks (range 7-10 weeks) after tumor cell implantation. No leakage of tumor cells and no soft part metastases occurred. Radiofrequency ablation was performed without complications. Imaging showed a complete ablation of the bone tumor in all rats. Histological findings confirmed a circular necrosis with an extensive destruction of tumor cells leaving a necrosis cavity. CONCLUSION: The experimental model presented here describes the first time the ability to carry out radiofrequency ablation in nude rats with intrafemoral induced osteolytic metastases of human breast cancer. RFA in human breast cancer cell line in nude rats is a feasible and useful possibility to evaluate and to test different RF-procedures. Additional treatment options like local chemotherapy or chemoembolization can be performed.

New prostheses for venous substitution.

In 81 Beagle dogs, 6 cm long segments of the inferior vena cava were replaced end-to-end by artificial vascular grafts (10 mm in diameter) without an av-fistula and anticoagulant drugs. Different graft materials have been used, such as various e-PTFE (30-90 microns fiber length) and polyurethane with low and increased microporosity. e-PTFE with 75 microns fiber length and polyurethane with increased porosity showed the best tissue incorporation, complete endothelialization of the whole length and a high patency rate of 80-85% after a follow-up of 12 months. In contrast to other commercially available vascular grafts (textile woven or knitted, e-PTFE 30 microns) tested in previous series, polyurethane and e-PTFE with increased microporosity had already achieved complete endothelialization after 6-12 weeks. Therefore, these optimized prostheses should be introduced into clinical practice for large venous substitution. Thereafter, an adjunctive av-fistula as protection is probably no longer necessary.

False aneurysm of the left femoral artery and thrombosis of the left femoral vein after total hip arthroplasty.

We report a 75-year-old male patient with an aneurysm of the left femoral artery after cemented total hip arthroplasty. Two months after the operation, the patient showed a spherical resistance and pain in the left groin. Examination showed a big false aneurysm of the left femoral artery. After resection of the aneurysm, an endovascular stent graft vessel prosthesis was implanted. The aneurysm originated from a punctual lesion of the artery caused by a screw. Since the first description of vessel lesions in orthopaedic surgery in 1964, a total of 24 cases of aneurysm in hip surgery have been described. Therefore, a review of literature tries to explain causes and mechanisms of vessel injuries in hip surgery and the possibilities of repair.

[Endooesophageal prostheses and their complications (author's transl)]. / Komplikationen nach Anwendung von Osophagus-Endoprothesen. Morphologische Untersuchungen.

After inserting an oesophageal prosthesis complications could be demonstrated in 53 cases (65%) from a total of 81 autopsies. Age distribution, tumour localisation and its relation to the development of local complications are analysed. Notwithstanding the high incidence of complications endoprostheses should be given preference to gastric fistulae.