FeSe with the PbO structure is a key member of the family of new high-Tc iron pnictide and chalcogenide superconductors, as while it possesses the basic layered structural motif of edge-sharing distorted FeSe4 tetrahedra, it lacks interleaved ion spacers or charge-reservoir layers. We find that application of hydrostatic pressure first rapidly increases Tc which attains a broad maximum of 37 K at ∼7 GPa (this is one of the highest Tc ever reported for a binary solid) before decreasing to 6 K upon further compression to ∼14 GPa. Complementary synchrotron X-ray diffraction at 16 K was used to measure the low-temperature isothermal compressibility of α-FeSe, revealing an extremely soft solid with a bulk modulus, K0 = 30.7(1.1) GPa and strong bonding anisotropy between inter-and intra-layer directions that transforms to the more densely packed β-polymorph above ∼9 GPa. The non-monotonic Tc(P ) behavior of FeSe coincides with drastic anomalies in the pressure evolution of the interlayer spacing, pointing to the key role of this structural feature in modulating the electronic properties. PACS numbers: 74.70.Dd, 74.25.Ha, 61.05.C-The α-polymorph of the simple binary FeSe phase has recently emerged as a superconductor with an ambient P T c of ∼8-13 K. 1,2 Its structure comprises stacks of edgesharing FeSe 4 tetrahedra with a packing motif essentially identical to that of the FeAs layers in the families of the FeAs-based high-T c superconductors 3,4,5,6,7 but lacking any interleaved ion spacers or insulating layers. The structural analogy is reinforced by the observation that below 70 K the high-temperature crystal structure becomes metrically orthorhombic (space group Cmma), 8 displaying an identical distortion of the FeSe layers to that observed in the iron oxyarsenide family. 9,10 Theoretical calculations also find a very similar 2D electronic structure to that of the FeAs-based superconductors with cylindrical electron sections at the zone corner and cylindrical hole surface sections. 11 Moreover, superconductivity in FeSe is very sensitive to defects and disorder and occurs over a limited range of FeSe 1−δ nonstoichiometry. 12The effect of applied pressure on T c provides crucial information in differentiating between competing models of superconductivity and in the FeSe binary, T c is initially extremely sensitive to P and rises rapidly to 27 K at 1.48 GPa. 2 At the same time, antiferromagnetic spin fluctuations present above T c are strongly enhanced by pressure. 13 In the FeAs-based superconductors, the response of T c to pressurization is complex and sensitively depends on the composition of the materials and their doping level. Both positive and negative initial pressure coefficients, dT c /dP have been measured. Typically for the REFeAsO 1−x F x families, dT c /dP is positive at low doping levels and switches over to a negative value as x increases. 14,15,16,17,18 Moreover, for systems where the initial dT c /dP is positive, there is a critical value of P above which the trend is reversed and T c then decreases...

We report structural, transport, and thermal properties of carrier-tuned Ba 8 Ga 16 Sn 30 single crystals with the type-1 clathrate structure ͑␤ phase͒, demonstrating that Ba 8 Ga 16 Sn 30 is a unique thermoelectric clathrate material wherein both the structure type and the carrier type are tunable. The results are compared with the properties of the better known type-8 structure ͑␣ phase͒ and of A 8 Ga 16 Ge 30 ͑A =Sr,Eu͒. Differential thermal analysis and powder x-ray diffraction show that both phases are stable up to their virtually identical melting point of 520Ϯ 3°C. Refinements of single-crystal x-ray diffraction data indicate that the Ba͑2͒ guest ion in the tetrakaidecahedron occupies the off-center 24k sites which are 0.43-0.44 Å away from the centered 6d site. The temperature-linear coefficient of the specific heat is 29 mJ/ mol K 2 for both n-and p-type carriers in the ␤ phase, four times larger than that for the ␣ phase, suggesting contributions from tunneling of the Ba͑2͒ guest ions between off-center minima. Analysis of specific heat with a soft-potential model ͑SPM͒ gives a characteristic energy of 20 K for the Ba͑2͒ vibration, significantly lower than 50 K for the ␣ phase and in fact the lowest among type-1 clathrates. The lattice thermal conductivities L for the ␤ phase with both charge carrier types are very similar and show a glasslike temperature dependence. This behavior in L ͑T͒ is also described using SPM analysis, where it is found that the coupling strength between guest modes and acoustic phonons for the ␤ phase is significantly larger than that for Sr 8 Ga 16 Ge 30 .

Summary Unsaturated fatty acids, including n-3 polyunsaturated fatty acids (PUFAs) such as docosahexaenoic acid (C225, DHA) and eicosapentaenoic acid (C20.5, EPA), and a series of n-6 PUFAs were investigated for their anti-tumour and antimetastatic effects in a subcutaneous (s.c.) implanted highly metastatic colon carcinoma 26 (Co 26Lu) model. EPA and DHA exerted significant inhibitory effects on tumour growth at the implantation site and significantly decreased the numbers of lung metastatic nodules. Oleic acid also significantly inhibited lung metastatic nodules. Treatment with arachidonic acid showed a tendency for reduction in colonization. However, treatment with high doses of fatty acids, especially linoleic acid, increased the numbers of lung metastatic nodules. DHA and EPA only inhibited lung colonizations when administered together with the tumour cells, suggesting that their incorporation is necessary for an influence to be exerted. Chromatography confirmed that contents of fatty acids in both tumour tissues and plasma were indeed affected by the treatments. Tumour cells pretreated with fatty acids in vivo, in particular DHA, also showed a low potential for lung colony formation when transferred to new hosts. Thus, DHA treatment exerted marked antimetastatic activity associated with pronounced change in the fatty acid component of tumour cells. The results indicate that uptake of DHA into tumour cells results in altered tumour cell membrane characteristics and a decreased ability to metastasize.Keywords: docosahexaenoic acid; unsaturated fatty acid; metastasis; colon carcinoma 26As tumour metastasis exerts an adverse influence on the prognosis of patients and is a major cause of cancer death, a considerable number of investigations into its biological, molecular and genetic features have been conducted (Raz and Ben-Ze'ev, 1987; Bertomeu et al, 1993). These investigations have indicated that tumour metastases are established by an inter-related sequence of processes, depending on various factors derived from both the tumour and the host. There is substantial evidence that the membrane properties of tumour cells play a major role in the interactions between themselves and the surrounding environment (Awad and Spector, 1976;Schroeder, 1984;Taraboletti et al, 1989;Dahiya et al, 1992). Studies on mice have revealed that plasma membranes of tumour sublines with high metastatic ability exhibit a more fluid state than those with low metastatic ability, based on differences in lipid composition and lipid-protein ratios (Kier and Franklin, 1991). Furthermore, studies have demonstrated that the chemical and physical properties of cell membranes are modified by both the amount and type of fat in the diet, and this influences growth and/or alters the metastatic ability of tumour cells (Chen et al, 1992;Rose and Hatala, 1994). Diets rich in linoleic acid have been found to enhance the growth and metastasis of transplantable mammary carcinomas in rodents (Rao and Abraham, 1976;. In a study of dietary n-3 PUFAs in a ...

Level IV, retrospective case series.