Low pressure reversibly driving colossal barocaloric effect in two-dimensional vdW alkylammonium halides.

Plastic crystals as barocaloric materials exhibit the large entropy change rivalling freon, however, the limited pressure-sensitivity and large hysteresis of phase transition hinder the colossal barocaloric effect accomplished reversibly at low pressure. Here we report reversible colossal barocaloric effect at low pressure in two-dimensional van-der-Waals alkylammonium halides. Via introducing long carbon chains in ammonium halide plastic crystals, two-dimensional structure forms in (CH3-(CH2)n-1)2NH2X (X: halogen element) with weak interlayer van-der-Waals force, which dictates interlayer expansion as large as 13% and consequently volume change as much as 12% during phase transition. Such anisotropic expansion provides sufficient space for carbon chains to undergo dramatic conformation disordering, which induces colossal entropy change with large pressure-sensitivity and small hysteresis. The record reversible colossal barocaloric effect with entropy change ΔSr ~ 400 J kg-1 K-1 at 0.08 GPa and adiabatic temperature change ΔTr ~ 11 K at 0.1 GPa highlights the design of novel barocaloric materials by engineering the dimensionality of plastic crystals.

Vitamin D receptor gene polymorphism, serum 25-hydroxyvitamin D levels, and risk of vitiligo: A meta-analysis.

OBJECTIVES: To explore the relationship among the vitamin D receptor (VDR) gene polymorphisms, serum 25-hydroxyvitamin D levels, and vitiligo. METHODS: Databases including PubMed, Cochrane Library, Ovid, Web of Science, CNKI, SinoMed, and Wanfang Data were systematically searched. The association was assessed using odds ratios (ORs), standard mean difference (SMD), and 95% confidence intervals (CIs). The statistical tests were performed using Review Manager 5.3.3. RESULTS: We identified a total of 17 studies. The relationship between VDR gene polymorphisms (BsmI, ApaI, TaqI, and FokI), serum 25 (OH)D levels, and incidence of vitiligo was investigated. The results of this meta-analysis showed that the dominant genetic model (CC+AC vs AA, P = .007, OR = 1.41, 95% CI = 1.10-1.80), recessive genetic model (CC vs AC+AA, P = .01, OR = 4.10, 95% CI = 1.36-12.35), and allelic contrast model (C vs A, P = .005, OR = 1.87, 95% CI = 1.21-2.90) of VDR Apal locus increased the risk of vitiligo, and BsmI, TaqI, and FokI loci and the risk of vitiligo have no obvious correlation. Serum 25 (OH)D deficiency was positively associated with the incidence of vitiligo (P < .0001, SMD = -0.94, 95% CI = -1.39, -0.48). CONCLUSION: This meta-analysis revealed that VDR Apal polymorphism increased the susceptibility risk of vitiligo, and there is a positive correlation between serum 25 (OH)D deficiency and the incidence of vitiligo.

Ultrathin SmCo5 nanoflakes with high-coercivity prepared by solid particle (NaCl) and surfactant co-assisted ball milling.

The ultrathin SmCo5 nanoflakes with average thickness smaller than 50 nm are prepared by a novel method of solid particle (NaCl) and surfactant co-assisted ball milling. The as-prepared nanoflakes exhibit a narrower thickness distribution of 10-50 nm and high coercivity of 23 kOe. The possible formation mechanism of nanoflakes are proposed. Temperature dependence of demagnetization curves indicate that the magnetization reversal may be controlled by both nucleation and pinning. The results of X-ray powder diffraction and magnetic measurement for aligned SmCo5 nanoflakes resin composite indicate that the nanoflakes have a high texture degree. The ultrathin thickness and high coercivity are beneficial for preparing the high performance soft/hard coupling magnets and nanocomposite magnets.

Giant barocaloric effect in hexagonal Ni2In-type Mn-Co-Ge-In compounds around room temperature.

The most widespread cooling techniques based on gas compression/expansion encounter environmental problems. Thus, tremendous effort has been dedicated to develop alternative cooling technique and search for solid state materials that show large caloric effects. An application of pressure to a material can cause a change in temperature, which is called the barocaloric effect. Here we report the giant barocaloric effect in a hexagonal Ni2In-type MnCoGe0.99In0.01 compound involving magnetostructural transformation, Tmstr, which is accompanied with a big difference in the internal energy due to a great negative lattice expansion(ΔV/V ~ 3.9%). High resolution neutron diffraction experiments reveal that the hydrostatic pressure can push the Tmstr to a lower temperature at a rate of 7.7 K/kbar, resulting in a giant barocaloric effect. The entropy change under a moderate pressure of 3 kbar reaches 52 J kg(-1) K(-1), which exceeds that of most materials, including the reported giant magnetocaloric effect driven by 5 T magnetic field that is available only by superconducting magnets.

Strong textured SmCo5 nanoflakes with ultrahigh coercivity prepared by multistep (three steps) surfactant-assisted ball milling.

The high coercivity of 26.2 kOe for SmCo5 nanoflakes are obtained by multistep (three steps) surfactant-assisted ball milling. The magnetic properties, phase structure and morphology are studied by VSM, XRD and SEM, respectively. The results demonstrate that the three step ball-milling can keep more complete crystallinity (relatively less defects) during the process of milling compared with one step high energy ball-milling, which enhances the texture degree and coercivity. In addition, the mechanism of coercivity are also studied by the temperature dependence of demagnetization curves for aligned SmCo5 nanoflakes/resin composite, the result indicates that the magnetization reversal could be controlled by co-existed mechanisms of pinning and nucleation.

Anisotropic modulation of magnetic properties and the memory effect in a wide-band (011)-Pr0.7Sr0.3MnO3/PMN-PT heterostructure.

Memory effect of electric-field control on magnetic behavior in magnetoelectric composite heterostructures has been a topic of interest for a long time. Although the piezostrain and its transfer across the interface of ferroelectric/ferromagnetic films are known to be important in realizing magnetoelectric coupling, the underlying mechanism for nonvolatile modulation of magnetic behaviors remains a challenge. Here, we report on the electric-field control of magnetic properties in wide-band (011)-Pr0.7Sr0.3MnO3/0.7Pb(Mg1/3Nb2/3)O3-0.3PbTiO3 heterostructures. By introducing an electric-field-induced in-plane anisotropic strain field during the cooling process from room temperature, we observe an in-plane anisotropic, nonvolatile modulation of magnetic properties in a wide-band Pr0.7Sr0.3MnO3 film at low temperatures. We attribute this anisotropic memory effect to the preferential seeding and growth of ferromagnetic (FM) domains under the anisotropic strain field. In addition, we find that the anisotropic, nonvolatile modulation of magnetic properties gradually diminishes as the temperature approaches FM transition, indicating that the nonvolatile memory effect is temperature dependent. By taking into account the competition between thermal energy and the potential barrier of the metastable magnetic state induced by the anisotropic strain field, this distinct memory effect is well explained, which provides a promising approach for designing novel electric-writing magnetic memories.

Giant negative thermal expansion in bonded MnCoGe-based compounds with Ni2In-type hexagonal structure.

MnCoGe-based compounds undergo a giant negative thermal expansion (NTE) during the martensitic structural transition from Ni2In-type hexagonal to TiNiSi-type orthorhombic structure. High-resolution neutron diffraction experiments revealed that the expansion of unit cell volume can be as large as ΔV/V ∼ 3.9%. The optimized compositions with concurrent magnetic and structural transitions have been studied for magnetocaloric effect. However, these materials have not been considered as NTE materials partially due to the limited temperature window of phase transition. The as-prepared MnCoGe-based compounds are quite brittle and naturally collapse into powders. By using a few percents (3-4%) of epoxy to bond the powders, we introduced residual stress in the bonded samples and thus realized the broadening of structural transition by utilizing the specific characteristics of lattice softening enforced by the stress. As a result, giant NTE (not only the linear NTE coefficient α but also the operation-temperature window) has been achieved. For example, the average α̅ as much as -51.5 × 10(-6)/K with an operating temperature window as wide as 210 K from 122 to 332 K has been observed in a bonded MnCo0.98Cr0.02Ge compound. Moreover, in the region between 250 and 305 K near room temperature, the α value (-119 × 10(-6)/K) remains nearly independent of temperature. Such an excellent performance exceeds that of most other materials reported previously, suggesting it can potentially be used as a NTE material, particularly for compensating the materials with large positive thermal expansions.

Abnormal percolative transport and colossal electroresistance induced by anisotropic strain in (011)-Pr(0.7)(Ca(0.6)Sr(0.4))(0.3)MnO3/PMN-PT heterostructure.

Abnormal percolative transport in inhomogeneous systems has drawn increasing interests due to its deviation from the conventional percolation picture. However, its nature is still ambiguous partly due to the difficulty in obtaining controllable abnormal percolative transport behaviors. Here, we report the first observation of electric-field-controlled abnormal percolative transport in (011)-Pr(0.7)(Ca(0.6)Sr(0.4))(0.3)MnO3/0.7Pb(Mg(1/3)Nb(2/3))O3-0.3PbTiO3 heterostructure. By introducing an electric-field-induced in-plane anisotropic strain-field in a phase separated PCSMO film, we stimulate a significant inverse thermal hysteresis (~ -17.5 K) and positive colossal electroresistance (~11460%), which is found to be crucially orientation-dependent and completely inconsistent with the well accepted conventional percolation picture. Further investigations reveal that such abnormal inverse hysteresis is strongly related to the preferential formation of ferromagnetic metallic domains caused by in-plane anisotropic strain-field. Meanwhile, it is found that the positive colossal electroresistance should be ascribed to the coactions between the anisotropic strain and the polarization effect from the poling of the substrate which leads to orientation and bias-polarity dependencies for the colossal electroresistance. This work unambiguously evidences the indispensable role of the anisotropic strain-field in driving the abnormal percolative transport and provides a new perspective for well understanding the percolation mechanism in inhomogeneous systems.

Biopsy from the base and edge of gastric ulcer healing or complete healing may lead to detection of gastric cancer earlier: an 8 years endoscopic follow-up study.

BACKGROUND/AIMS: To assess the incidence of gastric cancer development in gastric benign ulcer patients and to evaluate the value of biopsy by taking specimens from both the base and edges of ulcers in contrast to the traditional biopsy which takes specimens from the edges of ulcers only. METHODOLOGY: An endoscopic followup of more than 1 year was conducted on 456 gastric ulcer patients in our hospital for a duration over 8 years. We collected clinical, endoscopic and pathological data and obtained at least 6 biopsies from both the edges and the bases of ulcers healing or complete healing, respectively and assessed H. pylori infection. RESULTS: Gastric cancers developed in 11 (2.41%) of 456 GU patients. In the experimental group, 3 cases that were diagnosed by histology showed adenocarcinoma with specimens taken from the ulcer bases and in the other 5 cases the specimens were taken from the ulcer edges. The detection rate of gastric cancer from gastric ulcer between experimental group and control group was statistically significant (4.57% vs. 1.07%, p<0.05). CONCLUSIONS: Gastric ulcer may develop into gastric cancer over a certain period of time in patients infected with H. pylori. Biopsies from ulcer bases and edges at the second or subsequent endoscopies may lead to defection of gastric cancer earlier and more effectively than the biopsies which take specimens from the edges of ulcers only.

[Levels of transition on maternal transferred measles antibody in infants in 3 cities in China].

OBJECTIVE: To understand the epidemiological characteristics of age distribution of measles and related policies on measles vaccines (live; MV) in infants through analyzing the antibody levels of comparison in maternal-infant pairs. Transition of immunity in infants was also studied to provide theoretic basis for measles immunization strategy and to reduce the incidence of month-old infants. METHODS: In cities of Ningbo, Harbin, and Jinan from Zhejiang, Heilongjiang and Shandong provinces, data was collected from 2004 to 2007 and analyzed regarding the epidemic situation of measles. Studies on maternal-transferred measles antibody were carried our sero-epidemiologically. RESULTS: Most of the measles cases were found among babies younger than 12 months, and the incidence of < 1 year olds had been increasing. The distribution was dominated by 5 - 8 month olds in infant measles cases. The positive rate and GRMT of measles antibody in newborns were 89.3 percent and 738.93. The positive rate of the measles antibody and GMRT of the 6-month infant were 6.9% and 6.89, while 6.7% and 3.69 in 8-month infant. There was a declining trend of the positive rate of the measles antibody during the newborns to 8-month infant. The positive rate and GRMT of measles antibody in mothers were 84.3 percent and 516.94. Mother's measles antibodies mainly to be at low and moderate level, which accounted for 50.4 percent and 30.3 percent respectively, the correlation coefficient between mother and infant was 0.840. CONCLUSION: Maternal-transferred measles antibody decreased as the growth of infants. The positive rates of measles antibody were quite low in 6-month and 8-month olds which were the age range that needs most attention.

[Optical spectral verification of a harmful impurity to palladium catalyst].

The condensation of glyoxal with benzylamine leaded to hexabenzyl-hexaazaisowurtzitane (HBIW) with formic acid catalyst, and at the same time some side products were produced. Some impurities in HBIW would be harmful to the palladium catalyst used in the hydrogenolysis of HBIW, subsequently resulting in the low yield or failure of the catalytic reaction. The impurities in hexabenzylhexaazaisowurtzitane were distilled by means of recrystal technic, which were isolated by preparative chromatograph. The structure of the main impurity was studied with FTIR, 1H-NMR, ESI-MS, and element analysis. The result shows that the structure is comfirmed as N,N'-dibenzyl-oxalamide. which was synthesized in the way reported in the literature, and was charactered by FTIR, 1H-NMR and EI-MS. And the optical spectra data of the sample synthesized and the substance isolated from the impuries were the same, testifying that the substance isolated was N, N'-dibenzyl-oxalamide ulteriorly. N, N'-dibenzyl-oxalamide was added in the hydrogenolysis system of HBIW catalyzed by Pd catalyst. The result shows that N, N'-dibenzyl-oxalamide can reduce the activity of Pd catalyst, and when the quantity of N,N'-dibenzyl oxalmine added achievs 0.9% of the weight of HBIW, the reaction of catalytic hydrogenolysis fails.