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1.
Hum Reprod ; 35(1): 24-31, 2020 01 01.
Artículo en Inglés | MEDLINE | ID: mdl-31960907

RESUMEN

STUDY QUESTION: Is there an effect of male factor infertility (MFI) on either early or late morphokinetic parameters obtained during embryonic culture to blastocyst stage in a time-lapse imaging (TLI) incubator? SUMMARY ANSWER: Neither mild nor severe MFI had an impact on overall time to blastocyst or duration of individual cleavage stages in the total embryo population. WHAT IS KNOWN ALREADY: Prior studies have suggested that paternal DNA and sperm quality affect embryo morphokinetic parameters, but the impact of MFI is not fully understood. STUDY DESIGN, SIZE, DURATION: This retrospective cohort study, at a major academic fertility centre, included 536 couples (women, ≤44 years of age) undergoing IVF between September 2013 and September 2016. PARTICIPANTS/MATERIALS, SETTING, METHODS: Data from 4126 embryos cultured to the blastocyst stage in a TLI-monitored incubator were retrospectively reviewed. Embryos derived from the sperm of men with MFI were compared with those derived from patients with other infertility diagnoses. Generalized fixed and random effects models, t-test and χ2 were used as appropriate. MAIN RESULTS AND THE ROLE OF CHANCE: Couples with MFI had a higher rate of ICSI utilization and fewer usable embryos on average, and the men were older compared with couples with other diagnoses. Additionally, the women in MFI couples were younger and had higher antral follicle counts (AFCs) and higher anti-Müllerian hormone (AMH) levels compared with the other women undergoing IVF. When controlling for maternal and paternal ages, AMH and fertilization method (conventional IVF versus ICSI), neither mild nor severe MFI affected duration of individual cleavage stages or overall time to the blastocyst stage, when all or only usable embryos were examined (coefficient 0.44 hours in all embryos, P = 0.57; coefficient 0.39 hours in usable embryos, P = 0.60). Whether the sperm was surgically extracted similarly had no significant effect on embryo morphokinetic parameters. When the fertilization method was assessed independently, ICSI lengthened the overall time to blastocyst stage by 1.66 hours (P = 0.03) on average, primarily due to an increase in duration of the time from 5-cell embryo stage to early blastulation (P5SB). LIMITATIONS, REASONS FOR CAUTION: This large cohort study avoided embryo selection bias due to random assignment of embryos to the TLI incubators. However, our findings may not be generalizable to groups under-represented in our clinic population. Future studies should also evaluate the impact of male hormonal status and detailed sperm morphology, such as head versus flagellum defects, on embryo morphokinetic development. WIDER IMPLICATIONS OF THE FINDINGS: Our findings suggest that the fertilization method rather than MFI per se impacts time to early blastulation. The clinical implications of this effect on embryo development warrant further investigation. STUDY FUNDING/COMPETING INTEREST(S): There were no sources of funding for this study. There are no competing interests. TRIAL REGISTRATION NUMBER: N/A.


Asunto(s)
Blastocisto , Técnicas de Cultivo de Embriones , Estudios de Cohortes , Femenino , Fertilización In Vitro , Humanos , Masculino , Estudios Retrospectivos , Imagen de Lapso de Tiempo
2.
Leukemia ; 34(5): 1394-1406, 2020 05.
Artículo en Inglés | MEDLINE | ID: mdl-31811236

RESUMEN

The frailty index (FI) is based on the principle that the more deficits an individual has, the greater their risk of adverse outcomes. It is expressed as a ratio of the number of deficits present to the total number of deficits considered. We developed an MDS-specific FI using a prospective MDS registry and assessed its ability to add prognostic power to conventional prognostic scores in MDS. The 42 deficits included in this FI included measurements of physical performance, comorbidities, laboratory values, instrumental activities of daily living, quality of life and performance status. Of 644 patients, 440 were eligible for FI calculation. The median FI score was 0.25 (range 0.05-0.67), correlated with age and IPSS/IPSS-R risk scores and discriminated overall survival. With a follow-up of 20 months, survival was 27 months (95% CI 24-30.4). By multivariate analysis, age >70, FI, transfusion dependence, and IPSS were significant covariates associated with OS. The incremental discrimination improvement of the frailty index was 37%. We derived a prognostic score with five risk groups and distinct survivals ranging from 7.4 months to not yet reached. If externally validated, the MDS-FI could be used as a tool to refine the risk stratification of current clinical prognostication models.


Asunto(s)
Fragilidad/mortalidad , Fragilidad/patología , Síndromes Mielodisplásicos/mortalidad , Síndromes Mielodisplásicos/patología , Calidad de Vida , Sistema de Registros/estadística & datos numéricos , Medición de Riesgo/métodos , Actividades Cotidianas , Anciano , Anciano de 80 o más Años , Comorbilidad , Femenino , Estudios de Seguimiento , Humanos , Masculino , Persona de Mediana Edad , Pronóstico , Estudios Prospectivos , Factores de Riesgo , Tasa de Supervivencia
3.
Leuk Res ; 86: 106222, 2019 11.
Artículo en Inglés | MEDLINE | ID: mdl-31522038

RESUMEN

INTRODUCTION: Mouse double minute 2 protein (MDM2), a negative regulator of the p53 tumour suppressor gene, is frequently amplified in malignancies. MDM2 antagonists have shown efficacy in treating malignancies with MDM2 overexpression and can overcome chemoresistance in acute myeloid leukemia. We systematically evaluated the safety profile of MDM2 inhibitors in the treatment of solid organ and hematologic malignancies. MATERIALS AND METHODS: We searched Medline and EMBASE from January 1947 to November 2018 for prospective clinical studies, in English or French, investigating any MDM2 inhibitor in pediatric or adult cancers, and reporting dose and toxicity outcomes. Primary outcome was dose-limiting toxicity (DLT) and secondary outcome was death. RESULTS: The search yielded 493 non-duplicate citations. Eighteen studies of 10 inhibitors met inclusion criteria (total N = 1005 patients). Two-thirds of included studies did not define DLTs and the reporting of toxicities was highly variable. The most commonly reported DLTs were cytopenias, gastrointestinal toxicity, metabolic disturbances, fatigue and cardiovascular toxicity; there was one death attributed to treatment toxicity. CONCLUSION: MDM2 antagonists have been studied in a variety of malignancies with toxicities similar to other commonly used chemotherapy agents and may represent a safe adjuvant treatment for further study in in acute leukemia.


Asunto(s)
Antineoplásicos/efectos adversos , Efectos Colaterales y Reacciones Adversas Relacionados con Medicamentos/diagnóstico , Neoplasias Hematológicas/tratamiento farmacológico , Proteínas Proto-Oncogénicas c-mdm2/antagonistas & inhibidores , Efectos Colaterales y Reacciones Adversas Relacionados con Medicamentos/etiología , Estudios de Evaluación como Asunto , Neoplasias Hematológicas/patología , Humanos , Dosis Máxima Tolerada , Pronóstico
4.
J Assist Reprod Genet ; 35(5): 879-884, 2018 May.
Artículo en Inglés | MEDLINE | ID: mdl-29589293

RESUMEN

PURPOSE: To evaluate the differences in implantation and pregnancy rates when embryo transfer occurs on D2 versus D3 in women with a low yield of fertilized oocytes. METHODS: A total of 156 IVF/ICSI cycles from 141 women at an academic fertility center were analyzed in a retrospective fashion. Women with a low number of fertilized oocytes (≤ 2 two pronuclei (2PN) stage zygotes) who had their fresh embryo transfer on D2 or D3 were included in the study. Positive pregnancy test per IVF cycle (PPT), clinical pregnancy rate (CPR), spontaneous abortion rate (SABR), and implantation rate (IMPR) were the main outcome measures assessed. Mann-Whitney U test and χ2 test were used as appropriate. A generalized linear mixed effect model adjusted for relevant covariates was conducted. P < 0.05 was considered significant. RESULTS: Patients having their embryo transfer on D2, when compared to those who had a D3 embryo transfer, experienced similar PPT [30.8 vs. 28.2%, respectively; adjusted OR (95%CI): 0.49 (0.16, 1.52)], CPR [26.9 vs. 25.6%, respectively; adjusted OR (95%CI): 0.44 (0.12, 1.67)], and IMPR [17.3 vs. 16.7%, respectively; adjusted ß (95%CI) - 5.6% (- 15.0, 3.9)]. CONCLUSION: Our findings suggest that transferring embryos on D2 versus D3 in women with a limited number of 2PN stage zygotes does not affect early pregnancy outcomes. These results indicate that there can be some flexibility in scheduling the day of transfer at the convenience of both the patient and the center.


Asunto(s)
Transferencia de Embrión/métodos , Fertilización In Vitro/métodos , Aborto Espontáneo , Adulto , Implantación del Embrión , Femenino , Humanos , Recuperación del Oocito , Embarazo , Resultado del Embarazo , Índice de Embarazo , Estudios Retrospectivos , Factores de Tiempo
5.
Obes Rev ; 18(3): 370-379, 2017 03.
Artículo en Inglés | MEDLINE | ID: mdl-28112481

RESUMEN

Orthostatic intolerance (OI) is frequently the mechanism underlying the occurrence of noncardiac syncope (NCS) and is associated with substantial risk for injury. Body weight status appears to be a modifier of orthostatic responses and possibly influences the propensity to NCS. The majority of cross-sectional studies have found that the lower the body mass index (BMI) the greater the predisposition to OI is, accompanied with both down-regulation of sympathetic nervous system activity and up-regulation of parasympathetic nervous system activity. These changes appear to occur across the whole spectrum of BMI values from underweight to obesity, while they may be associated more strongly with central body fat than total body fat. Weight loss following bariatric surgery has been consistently found to increase OI, attributed first to the effects of weight loss per se, second to the specific type of surgical procedure and third to the potential postoperative autonomic neuropathy due to vitamin deficiency. The increased OI following bariatric surgery renders this intervention not easily tolerable for the affected individuals, mandating increased fluid and salt intake, pharmacological measures or surgical adjustments to attenuate OI. All future studies investigating orthostatic responses and NCS should implement a matching of the population arms for BMI and ideally for body fat.


Asunto(s)
Índice de Masa Corporal , Intolerancia Ortostática/fisiopatología , Síncope/fisiopatología , Pérdida de Peso , Adiposidad , Cirugía Bariátrica , Susceptibilidad a Enfermedades , Humanos , Obesidad/dietoterapia , Obesidad/cirugía
6.
Dalton Trans ; 44(46): 20207-15, 2015 Dec 14.
Artículo en Inglés | MEDLINE | ID: mdl-26537572

RESUMEN

High-spin square-planar molecular compounds are rare. In an effort to access this unique combination of geometry and spin state, we report the synthesis of a series of M(II) compounds stabilized by a trianionic pincer-type ligand, highlighting the formation of a high-spin square-planar Co(II) complex. Low-temperature, variable-frequency EPR measurements reveal that the ground electronic state of the Co(II) analogue is a highly anisotropic Kramers doublet (effective g values 7.35, 2.51, 1.48). This doublet can be identified with the lowest doublet of a quartet, S = 3/2 spin state that exhibits a very large ZFS, D ≥ 50 cm(-1). The observation of an effective g value considerably greater than the largest spin-only value 6, demonstrates that the orbital angular moment is essentially unquenched along one spatial direction. Density Functional Theory (DFT) and time-dependent DFT calculations reveal the electronic configurations of the ground and excited orbital states. A qualitative crystal field description of the geff tensor shows that it originates from the spin-orbit coupling acting on states obtained through the transfer of a ß electron from the doubly occupied xy to the singly-occupied {xz/yz} orbitals.


Asunto(s)
Cobalto/química , Complejos de Coordinación/química , Aniones/química , Complejos de Coordinación/síntesis química , Espectroscopía de Resonancia por Spin del Electrón , Electrones , Ligandos , Modelos Moleculares , Teoría Cuántica
7.
Chem Sci ; 6(1): 608-612, 2015 Jan 01.
Artículo en Inglés | MEDLINE | ID: mdl-28706628

RESUMEN

Square-planar high-spin Fe(ii) molecular compounds are rare and the only three non-macrocyclic or sterically-driven examples reported share a common FeO4 core. Using an easily modifiable pincer-type ligand, the successful synthesis of the first compound of this type that breaks the FeO4 motif was achieved. In addition, we present the first evidence that geometry and spin state persist in solution. Extensive characterization includes the first high-field EPR and variable field/temperature Mössbauer spectra for this class of compounds. Analysis of the spectroscopic data indicates this complex exhibits a large and positive zero-field splitting tensor. Furthermore, the unusually small ΔEQ value determined for this compound is rationalized on the basis of DFT calculations.

8.
Epidemiol Psychiatr Sci ; 23(3): 301-10, 2014 Sep.
Artículo en Inglés | MEDLINE | ID: mdl-23962651

RESUMEN

Background. Internet addiction disorder (IAD) is a novel concept under scrutiny for a definite inclusion in the psychiatric taxonomy, after showing correlations with overt expressions of psychopathology. This study aims to assist the scientific dialogue concerning IAD while presenting comparative data on adolescent psychopathology before and during a major economic crisis that has affected Greece from 2010 onwards. Methods. This is a cross-sectional study of a high school student population, aged 12-18, on IAD which follows-up a 2006 survey, and is carried out 5 years later at the same school classes. A comparison on psychopathological symptoms between the two samples is carried out to confirm any underlying correlations with IAD while providing some first insight on any effects of the economic crisis on adolescent psyche. Results. Results indicate that Internet addiction is increased in this population paralleling the increase in Internet availability at home. Adolescents affected with IAD present with more psychopathological symptoms. A comparison between the 2006 and 2011 samples reveals lower rates of general psychopathology but similar burden of reported symptoms. Conclusions. Those findings are discussed in the framework of adolescent coping to adversity, individual reactions to major crises, as well as the general debate regarding the value of IAD as a distinct diagnosis. The effects of the economic crisis may have triggered an adaptive response in the adolescent population although IAD as a distinct nosological entity is clearly linked to more symptoms of overt psychopathology. Directions are offered for further research in countries affected by crises.

9.
Obes Rev ; 14(12): 939-49, 2013 Dec.
Artículo en Inglés | MEDLINE | ID: mdl-23957239

RESUMEN

Adiponectin is secreted by the adipose tissue and it has been shown to be down-regulated in states of insulin resistance and in cardiovascular disease. It has also been found to be correlated with various parameters of lipoprotein metabolism, and in particular, it is associated with the metabolism of high-density lipoprotein (HDL) and triglycerides; adiponectin appears to induce an increase in serum HDL, and conversely, HDL can up-regulate adiponectin levels, and in addition, adiponectin lowers serum triglycerides through enhancement of the catabolism of triglyceride-rich lipoproteins. Studies investigating whether adiponectin is causally linked with lipoprotein metabolism have yielded conflicting data, and the mechanisms underlying the interplay between adiponectin and lipoproteins remain to be elucidated. The adiponectin-HDL relationship can explain at least in part the presumed protective role of adiponectin in cardiovascular disease and the adiponectin changes observed after dieting, exercise and lipid-lowering treatment. Statins, fibrates, niacin and n-3 fatty acids may influence circulating adiponectin levels, indicating that adiponectin may mediate some of the metabolic effects of these agents. Further studies to investigate more thoroughly the role of adiponectin in lipoprotein metabolism in the human setting should be carefully planned, focusing on causality and the possible impact of adiponectin on the pathogenesis of cardiovascular disease.


Asunto(s)
Adiponectina/metabolismo , Enfermedades Cardiovasculares/sangre , Enfermedades Cardiovasculares/prevención & control , Lipoproteínas HDL/metabolismo , Adiponectina/sangre , Humanos , Lipoproteínas HDL/sangre , Obesidad/sangre , Obesidad/prevención & control , Triglicéridos/sangre
10.
Transfus Med ; 23(2): 94-9, 2013 Apr.
Artículo en Inglés | MEDLINE | ID: mdl-23448208

RESUMEN

BACKGROUND: Red blood cell transfusion has been associated with adverse outcomes including infection, delayed recovery and increased mortality in some patient populations. Circulating cells that yield endothelial-like vascular progenitor cell (VPC) clusters are correlated with vascular repair and recovery after ischaemic injury. The impact of red cell transfusion on VPC clusters and vascular repair remains uncertain. STUDY DESIGN: We prospectively enrolled patients admitted to intensive care requiring red cell transfusion and subjects at low likelihood of requiring red cell transfusion. Levels of VPC clusters and plasma levels of angiogenic cytokines were compared. A total of 17 patients were recruited and had blood samples collected at time of enrolment and at 24-48 h, 48-72 h and 1 week following transfusion. RESULTS: We could not discern differences in the number of VPC clusters between transfused patients (n = 6) and non-transfused subjects (n = 11) at baseline or throughout the study period. VPC cluster levels demonstrated wide variance and were highest at 24-h post-enrolment in the entire cohort. Furthermore, levels of all 16 cytokines analysed were not significantly different between transfused and non-transfused patients and we did not observe a correlation between cytokine concentrations and levels of circulating VPC-cluster forming cells in the overall study population. CONCLUSIONS: Our data suggest that assessment of vascular repair responses after red blood cell transfusion in critically ill patients is challenging. Although our study did not allow us to discern an influence of red cell transfusion on VPC cluster levels or angiogenic cytokines, new methods evaluating vascular repair mechanisms may be required.


Asunto(s)
Inductores de la Angiogénesis/sangre , Citocinas/sangre , Células Endoteliales/citología , Transfusión de Eritrocitos , Regeneración , Células Madre/citología , Enfermedad Crítica , Femenino , Humanos , Masculino , Persona de Mediana Edad , Proyectos Piloto , Estudios Prospectivos
11.
Phys Rev Lett ; 110(8): 087205, 2013 Feb 22.
Artículo en Inglés | MEDLINE | ID: mdl-23473196

RESUMEN

We study the magnetic relaxation rate Γ of the single-molecule magnet Mn(12)-tBuAc as a function of the magnetic field component H(T) transverse to the molecule's easy axis. When the spin is near a magnetic quantum tunneling resonance, we find that Γ increases abruptly at certain values of H(T). These increases are observed just beyond values of H(T) at which a geometric-phase interference effect suppresses tunneling between two excited energy levels. The effect is washed out by rotating H(T) away from the spin's hard axis, thereby suppressing the interference effect. Detailed numerical calculations of Γ using the known spin Hamiltonian accurately reproduce the observed behavior. These results are the first experimental evidence for geometric-phase interference in a single-molecule magnet with true fourfold symmetry.

12.
Phys Rev Lett ; 110(20): 207203, 2013 May 17.
Artículo en Inglés | MEDLINE | ID: mdl-25167444

RESUMEN

The energy released in a magnetic material by reversing spins as they relax toward equilibrium can lead to a dynamical instability that ignites self-sustained rapid relaxation along a deflagration front that propagates at a constant subsonic speed. Using a trigger heat pulse and transverse and longitudinal magnetic fields, we investigate and control the crossover between thermally driven magnetic relaxation and magnetic deflagration in single crystals of Mn(12)-acetate.

13.
Horm Metab Res ; 44(1): 6-14, 2012 Jan.
Artículo en Inglés | MEDLINE | ID: mdl-22205567

RESUMEN

Retinol binding protein 4 (RBP(4)) is regarded as a novel cardiometabolic risk factor, which is secreted mainly by the hepatocytes and also by the adipose tissue. RBP(4) has been shown to induce insulin resistance, and plasma RBP(4) values are increased in type 2 diabetes mellitus, obesity, metabolic syndrome, and cardiovascular disease. Moreover, it has been found that circulating RBP(4) decreases during medical interventions that result in amelioration of the metabolic profile, such as diet, exercise, oral antidiabetic drugs, and hypolipidemic agents. However, only few of the RBP(4)-related studies have investigated whether RBP(4) constitutes a causal factor of the above-mentioned metabolic conditions. Importantly, circulating RBP(4) is influenced by some nonmetabolic conditions, such as renal failure, acute illness, injury, and liver failure. Thus, further studies investigating the metabolic roles of RBP(4) should be carefully planned, taking into account the effects of nonmetabolic conditions on circulating RBP(4).


Asunto(s)
Proteínas de Unión al Retinol/metabolismo , Animales , Enfermedades Cardiovasculares/metabolismo , Diabetes Mellitus Tipo 2/metabolismo , Humanos , Resistencia a la Insulina , Síndrome Metabólico/metabolismo , Obesidad/metabolismo
14.
Metab Syndr Relat Disord ; 8(2): 173-8, 2010 Apr.
Artículo en Inglés | MEDLINE | ID: mdl-20156072

RESUMEN

BACKGROUND: It is known that weight loss is beneficial for obese and overweight subjects with metabolic syndrome. Very few data exist, however, about whether the presence of metabolic syndrome and insulin resistance (IR) influence the response of these subjects to weight-reducing interventions. The current study intends to examine whether the presence of metabolic syndrome and its components could influence weight loss in obese and overweight women during a short-term, dietary-based intervention program. METHODS: A total of 107 women aged 49.1 +/- 13.5 years old, with a body mass index (BMI) greater than 25 were studied. The subjects were prescribed a low-fat diet plus weight-reducing drugs when necessary. RESULTS: After 3 months, the subjects with metabolic syndrome lost more weight than those without (6.62% vs. 4.50%; P < 0.05). There was a positive correlation between the percentage of weight loss and the number of the components of metabolic syndrome present at baseline (Spearman rho = 0.329; P < 0.01). Furthermore, patients in the quartile with the highest homeostasis model assessment index (HOMA-index) lost more weight than the remaining subjects (8.17% +/- 3.34 vs. 5.59% +/- 3.87; P < 0.05). These results were significant, even after adjustment for the medical treatment prescribed. CONCLUSIONS: Obese and overweight patients with metabolic syndrome showed a greater reduction of their body weight, compared to the patients without metabolic syndrome. The components of the metabolic syndrome present at baseline correlated positively with the percentage of the weight loss. Finally, the patients with the highest levels of HOMA-index at baseline lost significantly more weight than those with lower levels of this parameter.


Asunto(s)
Síndrome Metabólico/fisiopatología , Obesidad/dietoterapia , Obesidad/fisiopatología , Sobrepeso/dietoterapia , Sobrepeso/fisiopatología , Pérdida de Peso/fisiología , Adulto , Glucemia/análisis , Presión Sanguínea/fisiología , Índice de Masa Corporal , Dieta Reductora , Femenino , Humanos , Lípidos/sangre , Síndrome Metabólico/complicaciones , Persona de Mediana Edad , Obesidad/complicaciones , Sobrepeso/complicaciones
15.
Phys Rev Lett ; 102(15): 157202, 2009 Apr 17.
Artículo en Inglés | MEDLINE | ID: mdl-19518671

RESUMEN

The antiferromagnetic molecular wheel Fe18 of 18 exchange-coupled Fe;{III} ions has been studied by magnetic torque, magnetization, and inelastic neutron scattering. The combined data show that the low-temperature magnetism of Fe18 is very accurately described by the Néel-vector tunneling (NVT) scenario, as unfolded by semiclassical theory. In addition, the magnetic torque as a function of applied field exhibits oscillations that reflect the oscillations in the NVT splitting with field due to quantum phase interference.

16.
Phys Rev Lett ; 101(23): 237204, 2008 Dec 05.
Artículo en Inglés | MEDLINE | ID: mdl-19113589

RESUMEN

Magnetization measurements of a Mn12mda wheel single-molecule magnet with a spin ground state of S = 7 show resonant tunneling and quantum phase interference, which are established by studying the tunnel rates as a function of a transverse field applied along the hard magnetization axis. A Dzyaloshinskii-Moriya (DM) exchange interaction allows the tunneling between different spin multiplets. It is shown that the quantum phase interference of these transitions is strongly dependent on the direction of the DM vector.

17.
Phys Rev Lett ; 96(5): 057208, 2006 Feb 10.
Artículo en Inglés | MEDLINE | ID: mdl-16486979

RESUMEN

Magnetization measurements of a truly axial symmetry molecular nanomagnet with a spin ground state of S = 10 show resonant tunneling. This compound has the same magnetic anisotropy as but the molecules are better isolated and the crystals have less disorder and a higher symmetry. Hysteresis loop measurements at several temperatures reveal a well-resolved step fine structure which is due to level crossings of excited states. All step positions can be modeled by a simple spin Hamiltonian. The results establish a sharp crossover between thermally assisted and pure quantum tunneling, as had been previously predicted.

18.
Phys Rev Lett ; 95(14): 147201, 2005 Sep 30.
Artículo en Inglés | MEDLINE | ID: mdl-16241690

RESUMEN

Local time-resolved measurements of fast reversal of the magnetization of single crystals of Mn12-acetate indicate that the magnetization avalanche spreads as a narrow interface that propagates through the crystal at a constant velocity that is roughly 2 orders of magnitude smaller than the speed of sound. We argue that this phenomenon is closely analogous to the propagation of a flame front (deflagration) through a flammable chemical substance.

19.
Phys Rev Lett ; 95(3): 037203, 2005 Jul 15.
Artículo en Inglés | MEDLINE | ID: mdl-16090768

RESUMEN

Magnetization measurements of Mn12 molecular nanomagnets with spin ground states of S=10 and S=19/2 show resonance tunneling at avoided energy level crossings. The observed oscillations of the tunnel probability as a function of the magnetic field applied along the hard anisotropy axis are due to topological quantum phase interference of two tunnel paths of opposite windings. Spin-parity dependent tunneling is established by comparing the quantum phase interference of integer and half-integer spin systems.

20.
Inorg Chem ; 44(3): 502-11, 2005 Feb 07.
Artículo en Inglés | MEDLINE | ID: mdl-15679378

RESUMEN

The reaction of 2-(hydroxyethyl)pyridine (hepH) with a 2:1 molar mixture of [Mn3O(O2CMe)6(py)3]ClO4 and [Mn3O(O2CMe)6(py)3] in MeCN afforded the new mixed-valent (16Mn(III), 2Mn(II)), octadecanuclear complex [Mn18O14(O2CMe)18(hep)4(hepH)2(H2O)2](ClO4)2 (1) in 20% yield. Complex 1 crystallizes in the triclinic space group P. Direct current magnetic susceptibility studies in a 1.0 T field in the 5.0-300 K range, and variable-temperature variable-field dc magnetization studies in the 2.0-4.0 K and 2.0-5.0 T ranges were obtained on polycrystalline samples. Fitting of magnetization data established that complex 1 possesses a ground-state spin of S = 13 and D = -0.18 K. This was confirmed by the value of the in-phase ac magnetic susceptibility signal. Below 3 K, the complex exhibits a frequency-dependent drop in the in-phase signal, and a concomitant increase in the out-of-phase signal, consistent with slow magnetization relaxation on the ac time scale. This suggests the complex is a single-molecule magnet (SMM), and this was confirmed by hysteresis loops below 1 K in magnetization versus dc field sweeps on a single crystal. Alternating current and direct current magnetization data were combined to yield an Arrhenius plot from which was obtained the effective barrier (U(eff)) for magnetization reversal of 21.3 K. Below 0.2 K, the relaxation becomes temperature-independent, consistent with relaxation only by quantum tunneling of the magnetization (QTM) through the anisotropy barrier via the lowest-energy MS = +/-13 levels of the S = 13 spin manifold. Complex 1 is thus the SMM with the largest ground-state spin to display QTM.

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