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1.
Eur Rev Med Pharmacol Sci ; 26(17): 6300-6309, 2022 09.
Artículo en Inglés | MEDLINE | ID: mdl-36111931

RESUMEN

OBJECTIVE: Esophageal motility is regulated both by coordinated stimulation and inhibition of the circular and longitudinal muscle layers of the esophagus. Although there are many diseases known to have an effect on esophageal motility, the effect of subepithelial lesions (SELs) of the esophagus on esophageal motility, which is often detected incidentally, remains still unclear. The aim of this study is to reveal the effect of SELs of the esophagus on esophageal motility evaluating it by high-resolution manometry (HRM). PATIENTS AND METHODS: A total of 32 patients with SELs in the esophagus and 12 healthy individuals were included. All patients and controls included in the study underwent HRM using a Unisensor UniTip High Resolution catheter (Laborie, Amsterdam, Netherlands) and endosonographic examination. RESULTS: The mean age was 52.60±15.56 years (range: 23-79) and the average body mass index (BMI) was 26.63±4.71 kg/m2. Gender, height, weight, and BMI measurements, smoking status, alcohol use, and DM status did not statistically differ significantly between the groups (p>0.05). Of 32 patients with SELs, 65.6% (n=21) had lesions originating in the muscularis propria, while 34.4% had lesions originating in the submucosa. The rate of abnormal motility both in the supine and in upright positions of patients with SELs was found to be significantly higher than in the control group (p=0.001, p<0.01, respectively). In patients with SELs, the incidence of infective motility was higher than the normal group (p=0.001, p<0.01, respectively). As the size of the lesion increases (>2 cm), the probability of abnormal HRM results increased. CONCLUSIONS: SELs of the esophagus have pathological effects on esophageal motility, mainly ineffective esophageal motility disorder.


Asunto(s)
Trastornos de la Motilidad Esofágica , Adulto , Anciano , Endosonografía , Trastornos de la Motilidad Esofágica/diagnóstico por imagen , Humanos , Manometría/métodos , Persona de Mediana Edad , Cintigrafía
2.
Eur Rev Med Pharmacol Sci ; 26(14): 5178-5185, 2022 07.
Artículo en Inglés | MEDLINE | ID: mdl-35916815

RESUMEN

OBJECTIVE: Detection of the Kayser-Fleischer (KF) ring in the diagnostic scoring and treatment follow-up of Wilson's Disease (WD) is important. Slit lamp (SL) biomicroscopic examination has traditionally been used in the evaluation of the KF ring. The role of Anterior Segment Optical Coherence Tomography (AS-OCT), which is used in various corneal diseases, in the detection of KF rings has attracted attention in recent years. In our study, we tried to demonstrate the effectiveness of AS-OCT in detecting the KF ring by comparing it with SL biomicroscopic examination. PATIENTS AND METHODS: 64 of 356 patients followed in our outpatient clinic due to WD were included in the study in the order of their admission to the outpatient clinic. The KF ring was evaluated in both eyes by SL-biomicroscopic examination and AS-OCT. Ophthalmic examination, and findings were performed by the same physician. RESULTS: Age range was 18-67 years, mean 33.06±10.83 years, gender was 39.1% (n: 25) female. At the time of diagnosis, the mean age was 19.48 ± 9.36 years, range was minimum 5 years and maximum 51 years. Clinical presentation was mixed type involvement n: 18 (28.1%), hepatic involvement n: 32 (50%), neurological involvement n: 14 (21.9%). The follow-up period was 2-257 months (74.6±76.16). The presence of KF ring was evaluated together with both AS-OCT and slit-lamp examination, the presence of KF could be detected in both AS-OCT and SL biomicroscopic examination in 10 patients (15.6%), in 12 (18.8%) of the cases KF ring is positive in AS-OCT but was negative in Slit-lamp biomicroscopic examination, in 65.6 (n: 42) of the cases OCT and slit-lamp biomicroscopic examination results were negative. CONCLUSIONS: The sensitivity of AS-OCT in detecting the KF ring was higher than the slit-lamp biomicroscopic examination. AS-OCT can detect early stage of KF rings in Wilson's Disease patients, so that diagnosis and treatment accuracy can be evaluated effectively.


Asunto(s)
Enfermedades de la Córnea , Degeneración Hepatolenticular , Adolescente , Adulto , Anciano , Preescolar , Cobre , Enfermedades de la Córnea/diagnóstico por imagen , Femenino , Degeneración Hepatolenticular/diagnóstico por imagen , Degeneración Hepatolenticular/tratamiento farmacológico , Humanos , Persona de Mediana Edad , Tomografía de Coherencia Óptica/métodos , Adulto Joven
3.
Sci Rep ; 11(1): 22352, 2021 Nov 16.
Artículo en Inglés | MEDLINE | ID: mdl-34785675

RESUMEN

Unconventional superconductivity in non-centrosymmetric superconductors has attracted a considerable amount of attention. While several lanthanide-based materials have been reported previously, the number of actinide-based systems remains small. In this work, we present the discovery of a novel cubic complex non-centrosymmetric superconductor [Formula: see text] ([Formula: see text] space group). This intermetallic cage compound displays superconductivity below [Formula: see text] K, as evidenced by specific heat and resistivity data. [Formula: see text] is a type-II superconductor, which has an upper critical field [Formula: see text] T and a moderate Sommerfeld coefficient [Formula: see text] mJ [Formula: see text] [Formula: see text]. A non-zero density of states at the Fermi level is evident from metallic behavior in the normal state, as well as from electronic band structure calculations. The isostructural [Formula: see text] compound is a paramagnet with a moderately enhanced electronic mass, as indicated by the electronic specific heat coefficient [Formula: see text] mJ [Formula: see text] [Formula: see text] and Kadowaki-Woods ratio [Formula: see text] [Formula: see text] [Formula: see text] cm [Formula: see text] [Formula: see text] (mJ)[Formula: see text]. Both [Formula: see text] and [Formula: see text] are crystallographically complex, each hosting 212 atoms per unit cell.

4.
Eur Rev Med Pharmacol Sci ; 20(9): 1795-7, 2016 05.
Artículo en Inglés | MEDLINE | ID: mdl-27212172

RESUMEN

Proton pump inhibitors (PPI) metabolism and pharmacokinetics are regulated by cytochrome P450 enzymes in the liver. Cytochrome P450 2C19 (CYP2C19) polymorphism plays an import role in the metabolism of PPIs. The three possible genotypes for CYP2C19 each has a distinct effect on the pharmacodynamics of PPIs. Homozygote extensive metabolizers (HomEM) are the most frequent genotype and have two wild-types (non-mutant) (*1/*1) alleles. HomEM is associated with increased enzyme activity, which increases the rate of PPI metabolism. Intragastric pH, which is required for eradication, is lowest in HomEM. In HomEMs, an insufficient increase in intragastric pH results in decreased anti-Helicobacter pylori (HP) efficacy of the antibiotics and, therefore, lower eradication rates. We determined whether the HP eradication rate would increase after high-dose PPI treatment of extensive PPI metabolizers who had been treated unsuccessfully with a standard PPI dose. In our report, increasing the PPI dosage in patients with genotype polymorphisms may be effective on eradication rates. Eradication rates are directly affected by CYP2C19 polymorphisms, and eradication treatments should be planned considering such genotypic polymorphisms. Hence, CYP2C19 genotyping prior to treatment may facilitate determination of the optimum PPI dose to improve the therapeutic outcome. However, further researches are required to confirm this hypothesis.


Asunto(s)
Helicobacter pylori/efectos de los fármacos , Inhibidores de la Bomba de Protones/administración & dosificación , Citocromo P-450 CYP2C19/genética , Genotipo , Infecciones por Helicobacter/tratamiento farmacológico , Humanos
5.
Eur Rev Med Pharmacol Sci ; 20(5): 858-65, 2016 Mar.
Artículo en Inglés | MEDLINE | ID: mdl-27010142

RESUMEN

OBJECTIVE: Patients with inflammatory bowel disease (IBD) show increased the prevalence of cytomegalovirus (CMV) infection due to the severity of the disease and the immunosuppressive treatments they receive. The aim of this study was to determine the prevalence of CMV infection in IBD patients and identify the risk factors for CMV infection with different demographic characteristics in IBD patients. PATIENTS AND METHODS: We enrolled 85 patients diagnosed with IBD (43 with ulcerative colitis (UC) and 42 with Crohn's disease (CD)) in this prospective study. The clinical disease activities of UC and CD were assessed using Truelove-Witts and Crohn's disease activity index (CDAI). CMV infection was assessed by detection of DNA using real-time polymerase chain reaction (PCR) in blood samples and quantitative PCR in colonic biopsy specimens and by detection of inclusion bodies using hematoxylin-eosin staining. RESULTS: Thirteen patients with IBD exhibited concomitant CMV infection. CMV infection was not detected in any of the patients in remission. Viral loads measured in the colonic mucosa of infected patients ranged from 800-7000 genome copies/mL total extracted DNA. The mean serum CMV DNA level was 1694 ± 910 copies/mL (range: 800-3800). The rate of steroid resistance in CMV-positive cases was significantly higher than that in CMV-negative cases (p = 0.001). CD with acute exacerbation was a risk factor for CMV disease (p = 0.04). All of the CMV-positive patients received immunosuppressive treatments. CONCLUSIONS: CMV infection should be suspected in steroid-resistant UC and CD. Antiviral treatment improved the clinical outcome in steroid-resistant IBD cases with serum CMV DNA levels above 1000 copies/mL.


Asunto(s)
Infecciones por Citomegalovirus/epidemiología , Glucocorticoides/uso terapéutico , Inmunosupresores/uso terapéutico , Enfermedades Inflamatorias del Intestino/tratamiento farmacológico , Enfermedades Inflamatorias del Intestino/epidemiología , Adulto , Anciano , Antivirales/uso terapéutico , Infecciones por Citomegalovirus/etiología , Femenino , Humanos , Enfermedades Inflamatorias del Intestino/complicaciones , Masculino , Persona de Mediana Edad , Prevalencia , Factores de Riesgo , Insuficiencia del Tratamiento , Adulto Joven
6.
Eur Rev Med Pharmacol Sci ; 20(5): 879-85, 2016 Mar.
Artículo en Inglés | MEDLINE | ID: mdl-27010145

RESUMEN

OBJECTIVE: Cytochrome P450 2C19 (CYP2C19) polymorphisms play an important role in the metabolism of proton pump inhibitors. Rabeprazole is primarily metabolized via non-enzymatic pathways. In this study, we determined whether rabeprazole- and pantoprazole-based eradication treatments were influenced by CYP2C19 polymorphisms. PATIENTS AND METHODS: A total of 200 patients infected with Helicobacter pylori were treated with either 40 mg of pantoprazole or 20 mg of rabeprazole plus 500 mg of clarithromycin, 1000 mg of amoxicillin twice daily for 2 weeks. CYP2C19 genotype status was determined by Polymerase Chain Reaction (PCR)-restriction-fragment-length polymorphism. The genotypes of cytochrome P450 2C19 were classified as homozigote extensive metabolizer (HomEM), heterozigote metabolizer (HetEM) and poor metabolizer (PM). The CYP2C19 genotype of all patients, the effectiveness of the treatment, the effect of the genotypic polymorphism on the treatment were assessed. RESULTS: The frequencies of HotEM, HetEM, PM were 78%, 19.5% and 2.5%, respectively. 48% (n = 96) of the patients received treatment with rabeprazole and 52% (n = 104) with pantoprazole. The eradication rate was 64.7% for HomEM, 79.4% for HetEM, 100% for PM (p = 0.06). In HetEM, PM, are considered as a single group, the eradication rates were higher in patients with the HetEM and PM (HetEM+PM) genotypes than in those with the wild-type genotype (81.8 vs. 64.7% p = 0.031). Among the patients treated with rabeprazole, the eradication rates were significantly lower in those with the HomEM genotype than in those with the HetEM+PM genotypes (60% vs. 85.7% p = 0.023). CONCLUSIONS: The genotypic polymorphism is effective on the rate of eradication. Eradication treatment rate with rabeprazole is influenced by CYP2C19 genotype.


Asunto(s)
2-Piridinilmetilsulfinilbencimidazoles/administración & dosificación , Citocromo P-450 CYP2C19/genética , Infecciones por Helicobacter/tratamiento farmacológico , Infecciones por Helicobacter/genética , Polimorfismo de Longitud del Fragmento de Restricción , Rabeprazol/administración & dosificación , Adolescente , Adulto , Anciano , Amoxicilina/administración & dosificación , Claritromicina/administración & dosificación , Quimioterapia Combinada , Femenino , Genotipo , Helicobacter pylori/efectos de los fármacos , Humanos , Masculino , Persona de Mediana Edad , Omeprazol/administración & dosificación , Pantoprazol , Inhibidores de la Bomba de Protones/administración & dosificación , Adulto Joven
7.
Dalton Trans ; 44(16): 7524-37, 2015 Apr 28.
Artículo en Inglés | MEDLINE | ID: mdl-25805335

RESUMEN

We present the evolution of the low-temperature thermodynamic, galvanomagnetic and thermoelectric properties of the type-I clathrate Ba8Ni(x)Ge(46-x-y□y) with the Ni concentration studied on polycrystalline samples with 0.0 ≤ x ≤ 6.0 by means of specific heat, Hall effect, electrical resistivity, thermopower and thermal conductivity measurements in the 2-350 K temperature range and supported by first-principles calculations. The experimental results evidence a 2a × 2a × 2a supercell described in the space group Ia3d for x ≤ 1.0 and a primitive unit cell a × a × a (space group Pm3n) above this Ni content. This concentration also marks the limit between a regime where both electrons and holes contribute to the electrical conduction (x ≤ 1.0) and a conventional, single-carrier regime (x > 1.0). This evolution is traced by the variations in the thermopower and Hall effect with x. In agreement with band structure calculations, increasing the Ni content drives the system from a nearly-compensated semimetallic state (x = 0.0) towards a narrow-band-gap semiconducting state (x = 4.0). A crossover from an n-type to a p-type conduction occurs when crossing the x = 4.0 concentration i.e. for x = 4.1. The solid solution Ba8Ni(x)Ge(46-x-y□y) therefore provides an excellent experimental platform to probe the evolution of the peculiar properties of the parent type-I clathrate Ba8Ge43□3 upon Ge/Ni substitution and filling up of the vacancies, which might be universal among the ternary systems at low substitution levels.

8.
J Phys Condens Matter ; 26(48): 485801, 2014 Dec 03.
Artículo en Inglés | MEDLINE | ID: mdl-25373324

RESUMEN

Polycrystalline samples of the type-I clathrate Ba(8)Ni(x)Ge(46-x-y)□(y) were synthesized for 0.2 ⩽ x ⩽ 3.5 by melt quenching and for 3.5

9.
Genet Couns ; 25(2): 231-5, 2014.
Artículo en Inglés | MEDLINE | ID: mdl-25059024

RESUMEN

The VATER/VACTERL association is typically defined by the presence of at least three of the following congenital malformations: vertebral anomalies, anal atresia, cardiac malformations, tracheo-esophageal fistula, renal anomalies, and limb abnormalities (13). We report a rare case of a monochorionic twin gestation in which one of the infants had VACTERL association. Antenatal ultrasound showed bilateral renal dysplasia and cardiac anomaly (ASD) in twin A. Twin A was noted to have the following anomalies: a single umbilical artery, limb anomaly (right hand preaxial polydactyly), vertebral anomalies (T9 and T11 butterfly vertebras, bilateral renal agenesis, bladder agenesis, anal and urethral atresia. A normal-sized stomach and normal amount of amniotic fluid were observed during the prenatal period with no other anomalies. Twin B (male) was healthy and no cardiac, renal, or congenital anomalies were demonstrated on ultrasound and physical examination. Infant A was also diagnosed as having VACTERL association because he had five of the core anomalies (V, A, C, R, L) of VACTERL association. Butterfly vertebra is an uncommon congenital spinal anomaly. To the best of our knowledge, our patient is the second case VACTERL association with butterfly vertebra in the literature.


Asunto(s)
Canal Anal/anomalías , Esófago/anomalías , Cardiopatías Congénitas/patología , Riñón/anomalías , Deformidades Congénitas de las Extremidades/patología , Columna Vertebral/anomalías , Tráquea/anomalías , Gemelos Monocigóticos , Canal Anal/patología , Canal Anal/cirugía , Esófago/patología , Esófago/cirugía , Resultado Fatal , Cardiopatías Congénitas/cirugía , Humanos , Recién Nacido , Riñón/patología , Riñón/cirugía , Deformidades Congénitas de las Extremidades/cirugía , Masculino , Columna Vertebral/patología , Columna Vertebral/cirugía , Tráquea/patología , Tráquea/cirugía , Ultrasonografía Prenatal
10.
Genet Couns ; 25(1): 49-52, 2014.
Artículo en Inglés | MEDLINE | ID: mdl-24783655

RESUMEN

We report a case of a female baby born at 34 weeks of gestation. Birth weight was 1760 g (10th-25th centile), length 41cm (10th-25th centile) and head circumference 27cm (< 10th centile). Clinical examination revealed microcephaly, hypotelorism, micrognathia, a flat rudimentary nose, high palate, thick dysplastic low-set ears, a short neck, preaxial polydactyly of the right hand, and overriding toes. Investigations showed bilateral congenital glaucoma, alobar holoprosencephaly, severe ventriculomegaly and absence midline structures of the brain, a large atrial septal defect. The karyotype was 46,XX. The case was also diagnosed as having holoprosencephaly-polydactyly syndrome (pseudotrisomy 13) because she had alobar holoprosencephaly, preaxial polydactyly, facial dysmorfism (hypotelorism, micrognathia, a flat rudimentary nose, high palate, thick dysplastic low-set ears) and normal karyotype.


Asunto(s)
Anomalías Múltiples/patología , Macrosomía Fetal/patología , Glaucoma/congénito , Deformidades Congénitas de la Mano/patología , Holoprosencefalia/patología , Polidactilia/patología , Trisomía/patología , Cromosomas Humanos Par 13 , Femenino , Edad Gestacional , Humanos , Recién Nacido , Recien Nacido Prematuro , Pulgar/anomalías
11.
J Viral Hepat ; 21(2): 111-20, 2014 Feb.
Artículo en Inglés | MEDLINE | ID: mdl-24383924

RESUMEN

Chronic hepatitis C (CHC) patients with treatment failure (TF) remain at risk of continuing fibrosis progression. However, it has not been investigated whether there is an increased risk of accelerated fibrosis progression after failed interferon-based therapy. We aimed to investigate long-term influence of TF on fibrosis progression compared with untreated patients with CHC. We studied 125 patients with CHC who underwent paired liver biopsies from 1994 to 2012. Patients with advanced fibrosis were excluded from the analysis. Sixty-three patients had TF, and 62 patients were treatment-naïve (TN). Annual fibrosis progression rate (FPR) was calculated, and significant fibrosis progression (SFP) was defined as ≥ 2 stage increase in fibrosis during follow-up. Multiple regression analyses were performed to find out independent predictors of FPR and SFP. Demographic characteristics and duration between paired liver biopsies were similar in TF and TN groups. Baseline alanine aminotransferase and gamma-glutamyl transferase (GGT) levels (71 ± 31 vs 47 ± 22, P < 0.001 and 49 ± 39 vs 36 ± 28, P = 0.027, respectively), baseline mean fibrosis stage (2.2 ± 0.7 vs 1.9 ± 0.7, P = 0.018) and histologic activity index (6.3 ± 1.9 vs 4.3 ± 1.6, P < 0.001) were higher in the TF group compared with the TN group. In regression analyses, the strongest independent predictor of fibrosis progression was the GGT level (OR: 1.03, 95%CI 1.01-1.5, P < 0.001). Treatment experience (OR: 5.97, 95%CI 1.81-19.7, P = 0.003) also appeared as an independent predictor of both FPR and SFP. Failed interferon-based CHC treatment may lead to accelerated FPR in the long-term compared with the natural course.


Asunto(s)
Antivirales/uso terapéutico , Hepatitis C Crónica/complicaciones , Hepatitis C Crónica/tratamiento farmacológico , Cirrosis Hepática/epidemiología , Adulto , Alanina Transaminasa/sangre , Estudios de Cohortes , Progresión de la Enfermedad , Femenino , Hepatitis C Crónica/patología , Histocitoquímica , Humanos , Cirrosis Hepática/patología , Masculino , Persona de Mediana Edad , Insuficiencia del Tratamiento , gamma-Glutamiltransferasa/sangre
12.
Tumour Biol ; 35(3): 2327-33, 2014 Mar.
Artículo en Inglés | MEDLINE | ID: mdl-24142532

RESUMEN

Hepatocellular carcinoma (HCC) is the commonest primary malignant cancer of the liver in the world. This study was conducted to investigate the serum levels of hepatocyte growth factor (HGF)in HCC patients and the relationship with tumor progression and known prognostic parameters. Fifty-four patients with HCC were investigated. Pretreatment HGF levels were employed the quantitative sandwich enzyme immunoassay technique (ELISA). Age and sex matched 20 healthy controls were included in the analysis. The median age of the patients was 60 years (range 36-77 years); where males consistituted of majority of the group (88.8%). All of patients had cirrhotic history. Fourty-six percent (n = 25) of patients had Child-Pugh Score A, 30% (n = 16) had Score B or C. All of the patients were treated with local therapies but none of them received sorafenib. The baseline serum HGF levels were significantly higher in patients with HCC than in the control group (p < 0.001). Male patients had higher serum HGF levels compared with female patients (p = 0.01). Serum HGF levels were significantly higher in the patients with elevated serum ALT levels than others with normal serum ALT levels (p = 0.05). Poor performance status (p < 0.001), viral etiology of cirrhosis (p = 0.03), larger tumor size (p = 0.01), lower serum hemogloblin levels (p = 0.03), and not be treated for HCC (p = 0.001) related to worse survival. However, serum HGF did not have significantly adverse effect on survival (p = 0.58). Despite serum HGF levels were found diagnostic value, serum HGF levels had no prognostic value in patients with HCC.


Asunto(s)
Carcinoma Hepatocelular/sangre , Factor de Crecimiento de Hepatocito/sangre , Neoplasias Hepáticas/sangre , Adulto , Anciano , Biomarcadores de Tumor/sangre , Carcinoma Hepatocelular/diagnóstico , Carcinoma Hepatocelular/mortalidad , Ensayo de Inmunoadsorción Enzimática , Femenino , Humanos , Estimación de Kaplan-Meier , Neoplasias Hepáticas/diagnóstico , Neoplasias Hepáticas/mortalidad , Masculino , Persona de Mediana Edad , Pronóstico
13.
Genet Couns ; 24(3): 279-82, 2013.
Artículo en Inglés | MEDLINE | ID: mdl-24341142

RESUMEN

Bamforth syndrome is a rare inherited condition whose main features are congenital hypothyroidism due to thyroid dysplasia, cleft palate, and spiky hair, with or without choanal atresia and bifid epiglottis. This syndrome is caused by mutations in the gene encoding thyroid transcription factor 2 (TTF-2). Here we report on a newborn with facial dysmorphism, cleft palate, spiky hair, congenital hypothyroidism and that are observed with Bamforth syndrome. This is the first case with Bamforth syndrome in which porencephaly has been observed.


Asunto(s)
Encefalopatías/etiología , Fisura del Paladar/complicaciones , Colágeno Tipo IV/deficiencia , Enfermedades del Cabello/complicaciones , Hemiplejía/etiología , Hipotiroidismo/complicaciones , Anomalías Múltiples/diagnóstico , Encéfalo/patología , Encefalopatías/diagnóstico , Fisura del Paladar/diagnóstico , Consanguinidad , Enfermedades del Cabello/diagnóstico , Hemiplejía/diagnóstico , Humanos , Hipotiroidismo/diagnóstico , Recién Nacido , Imagen por Resonancia Magnética/métodos , Masculino , Examen Físico/métodos , Porencefalia
14.
Genet Couns ; 24(2): 217-22, 2013.
Artículo en Inglés | MEDLINE | ID: mdl-24032293

RESUMEN

The 4q deletion syndrome is a rare chromosome deletion syndrome with a wide range of clinical phenotypes. Herein we report cases of twins (karyotype 46, XY) carrying terminal deletion of the chromosome 4 (q31qter) segment resulting in craniofacial dysmorphism, skeletal anomalies, ocular findings and cardiac defect.


Asunto(s)
Anomalías Múltiples/genética , Trastornos de los Cromosomas/genética , Enfermedades en Gemelos/genética , Deleción Cromosómica , Trastornos de los Cromosomas/patología , Trastornos de los Cromosomas/fisiopatología , Cromosomas Humanos Par 4/genética , Edad Gestacional , Humanos , Recién Nacido , Masculino , Turquía
15.
Inorg Chem ; 52(17): 9720-6, 2013 Sep 03.
Artículo en Inglés | MEDLINE | ID: mdl-23944652

RESUMEN

Type-I clathrates Rb(8-x-t)K(x□t)Au(y)Ge(46-y) are synthesized from Rb4Ge9, K4Ge9, Au, and Ge. Crystal structures and compositions are determined by single-crystal and powder X-ray diffraction methods. The lattice parameters are 10.8103(2), 10.7956(2), 10.7850(2), and 10.7723(2) Šin space group Pm3n for Rb7.88(2)Au2.47(2)Ge43.53(2), Rb3.69(4)K4.31(4)Au2.17(2)Ge43.83(2), Rb1.66(5)K6.34(5)Au2.17(1)Ge43.83(1), and K6.71(4)Au2.28(2)Ge43.72(2), respectively. Bonding analysis for Rb8Au6Ge40 suggests ionic interaction of Rb with the framework besides covalent interactions between Ge and Au/Ge. Rb7.88Au2.47Ge43.53 and K6.71(4)Au2.28Ge43.72 are both diamagnetic. The heat capacity of K6.71Au2.28Ge43.72 is analyzed. Transport properties of Rb7.88Au2.47Ge43.53 reveal n-type conducting, and low thermal conductivity.

16.
Chemistry ; 18(20): 6272-83, 2012 May 14.
Artículo en Inglés | MEDLINE | ID: mdl-22461109

RESUMEN

The synthesis and a joint experimental and theoretical study of the crystal structure and physical properties of the new ternary intermetallic compound TiGePt are presented. Upon heating, TiGePt exhibits an unusual structural phase transition with a huge volume contraction of about 10 %. The transformation is characterized by a strong change in the physical properties, in particular, by an insulator-metal transition. At temperatures below 885 °C TiGePt crystallizes in the cubic MgAgAs (half-Heusler) type (LT phase, space group F43m, a = 5.9349(2) Å). At elevated temperatures, the crystal structure of TiGePt transforms into the TiNiSi structure type (HT phase, space group Pnma, a = 6.38134(9) Å, b = 3.89081(5) Å, c = 7.5034(1) Å). The reversible, temperature-dependent structural transition was investigated by in-situ neutron powder diffraction and dilatometry measurements. The insulator-metal transition, indicated by resistivity measurements, is in accord with band structure calculations yielding a gap of about 0.9 eV for the LT phase and a metallic HT phase. Detailed analysis of the chemical bonding in both modifications revealed an essential change of the Ti-Pt and Ti-Ge interactions as the origin of the dramatic changes in the physical properties.

17.
Inorg Chem ; 51(8): 4730-41, 2012 Apr 16.
Artículo en Inglés | MEDLINE | ID: mdl-22455546

RESUMEN

Type-I clathrate phase Ba(8)Ni(x)□(y)Si(46-x-y) (□ = vacancy) was obtained from the elements at 1000 °C with the homogeneity range 2.4 ≤ x ≤ 3.8 and 0 ≤ y ≤ 0.9. In addition, samples with low Ni content (x = 1.4 and 1.6; y = 0) and small Ba deficiency were prepared from the melt by steel-quenching. Compositions were established by microprobe analysis and crystal structure determination. Ba(8-δ)Ni(x)□(y)Si(46-x-y) crystallizes in the space group Pm ̅3n (No. 223) with lattice parameter ranging from a = 10.3088(1) Å for Ba(7.9(1))Ni(1.4(1))Si(44.6(1)) to a = 10.2896(1) Å for Ba(8.00(3))Ni(3.82(4))Si(41.33(6)). Single-crystal X-ray diffraction data together with microprobe analysis indicate an increasing number of framework vacancies toward compositions with higher Ni content. For all compositions investigated, Ni K-edge X-ray absorption spectroscopy measurements showed an electronic state close to that of elemental Ni. All samples exhibit metallic-like behavior with moderate thermopower and low thermal conductivity in the temperature range 300-773 K. Samples with compositions Ba(7.9(1))Ni(1.4(1))Si(44.6(1)) and Ba(7.9(1))Ni(1.6(1))Si(44.4(1)) are superconducting with T(c) values of 6.0 and 5.5 K, respectively.

19.
Dalton Trans ; 39(4): 1078-88, 2010 Jan 28.
Artículo en Inglés | MEDLINE | ID: mdl-20066194

RESUMEN

The single phase clathrate-I Ba(8)Ge(43)square(3) (space group Ia3d (no. 230), a = 21.307(1) A) was synthesized by quenching the melt between cold steel plates. Specimens for physical property measurements were characterized by microstructure analysis and X-ray diffraction on polycrystalline samples as well as single crystals. Transport properties including thermopower, electrical resistivity, thermal conductivity and specific heat were investigated in a temperature range of 2-673 K. The electrical resistivity exhibits a metal-like temperature dependence below 300 K turning into a semiconductor-like behaviour above 300 K. The analysis of the specific heat at low temperature indicates a finite density of states at the Fermi level, thus corroborating the metallic character below 300 K. The temperature dependence of the specific heat was modelled assuming Einstein-like localized vibrations of Ba atoms inside the cages of the Ge framework. A conventional crystal-like behaviour of the thermal conductivity with a low lattice contribution (kappa(l)(300 K) = 2.7 W m(-1) K(-1)) has been evidenced.

20.
J Phys Chem A ; 110(3): 1100-5, 2006 Jan 26.
Artículo en Inglés | MEDLINE | ID: mdl-16420014

RESUMEN

The electron localization function (ELF) is implemented in the first-principles, all-electron, full-potential local orbital method. This full-potential implementation increases the accuracy with which the ELF can be computed for crystalline materials. Some representative results obtained are presented and compared with the results of other methods. Although for crystal structures with directed bonding only minor differences are found, in simple elemental metals, there are differences in the valence region, which give rise to different ELF topologies.

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