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1.
Nature ; 554(7692): 337-340, 2018 02 14.
Artículo en Inglés | MEDLINE | ID: mdl-29446380

RESUMEN

Auroral substorms, dynamic phenomena that occur in the upper atmosphere at night, are caused by global reconfiguration of the magnetosphere, which releases stored solar wind energy. These storms are characterized by auroral brightening from dusk to midnight, followed by violent motions of distinct auroral arcs that suddenly break up, and the subsequent emergence of diffuse, pulsating auroral patches at dawn. Pulsating aurorae, which are quasiperiodic, blinking patches of light tens to hundreds of kilometres across, appear at altitudes of about 100 kilometres in the high-latitude regions of both hemispheres, and multiple patches often cover the entire sky. This auroral pulsation, with periods of several to tens of seconds, is generated by the intermittent precipitation of energetic electrons (several to tens of kiloelectronvolts) arriving from the magnetosphere and colliding with the atoms and molecules of the upper atmosphere. A possible cause of this precipitation is the interaction between magnetospheric electrons and electromagnetic waves called whistler-mode chorus waves. However, no direct observational evidence of this interaction has been obtained so far. Here we report that energetic electrons are scattered by chorus waves, resulting in their precipitation. Our observations were made in March 2017 with a magnetospheric spacecraft equipped with a high-angular-resolution electron sensor and electromagnetic field instruments. The measured quasiperiodic precipitating electron flux was sufficiently intense to generate a pulsating aurora, which was indeed simultaneously observed by a ground auroral imager.

2.
Acta Orthop Belg ; 89(3): 469-475, 2023 Sep.
Artículo en Inglés | MEDLINE | ID: mdl-37935231

RESUMEN

Intravenous acetaminophen is an integral component of multimodal postoperative pain management. This prospective study aims to assess the efficacy of the repeated administration of intravenous acetaminophen and the impact on postoperative patient satisfaction with postoperative pain management after total knee arthroplasty (TKA). We enrolled 98 patients scheduled for unilateral TKA. Patients were randomly assigned to receive either 1000 mg of intravenous acetaminophen at 6-hour intervals (AAP group) or not to receive intravenous acetaminophen (control group). All patients underwent single-shot femoral nerve block after general anesthesia, as well as intraoperative periarticular infiltration of analgesia prior to implantation. The primary outcome was the postoperative numerical rating scale (NRS) pain score at rest. The NRS score was measured just before the administration of study drugs, immediately after arrival in the ward (time 0), and at 6, 12, 18, 24, and 48 h (time 1 to time 5, respectively) postoperatively. We also evaluated the mean doses of rescue opioid use for 24 h postoperatively. At time 5, the AAP group had significantly improved mean NRS score than controls (3.0 vs. 4.0; P < 0.01). Rescue opioid use was significantly lower in the AAP group for 24 hours compared to controls (0.3 µg vs. 0.9 µg; P < 0.01). Repeated intravenous acetaminophen administration after TKA may provide better analgesia and reduce opioid use.


Asunto(s)
Acetaminofén , Artroplastia de Reemplazo de Rodilla , Humanos , Acetaminofén/uso terapéutico , Manejo del Dolor , Artroplastia de Reemplazo de Rodilla/efectos adversos , Analgésicos Opioides/uso terapéutico , Estudios Prospectivos , Dolor Postoperatorio/tratamiento farmacológico
3.
Clin Exp Obstet Gynecol ; 44(2): 216-219, 2017.
Artículo en Inglés | MEDLINE | ID: mdl-29746025

RESUMEN

A short umbilical cord is associated with adverse pregnancy outcomes. However, there is no universally accepted definition of a short cord. OBJECTIVE: This study aimed to determine the umbilical cord length showing the highest correlation with adverse pregnancy outcomes. MATERIALS AND METHODS: The authors retrospectively analyzed the clinical data of women who attempted vaginal birth in the present institution. Umbilical cord lengths were categorized into three groups: less than the first percentile, from the first percentile to less than the tenth percentile, and others. Maternal and neonatal characteristics previously suggested to affect cord length were evaluated. The main outcome was the rate of cesarean delivery. The authors also evaluated the frequency of operative vaginal delivery, small-for-gestational-age (SGA) births, neonatal intensive care unit (NICU) admission, umbilical artery pH < 7.1, and abnormal bleeding during delivery. RESULTS: Cord lengths of 35 and 45 cm corresponded to the first and tenth percentiles, respectively. A short cord was an indi- cator of unplanned cesarean delivery and small-for-gestational-age births. CONCLUSION: An umbilical cord length of ≤ 45 cm is a clinically useful indicator of adverse pregnancy outcomes.


Asunto(s)
Cesárea/estadística & datos numéricos , Sangre Fetal/química , Complicaciones del Trabajo de Parto , Resultado del Embarazo/epidemiología , Cordón Umbilical/patología , Adulto , Femenino , Humanos , Concentración de Iones de Hidrógeno , Recién Nacido , Recién Nacido Pequeño para la Edad Gestacional , Unidades de Cuidado Intensivo Neonatal/estadística & datos numéricos , Japón/epidemiología , Complicaciones del Trabajo de Parto/diagnóstico , Complicaciones del Trabajo de Parto/epidemiología , Complicaciones del Trabajo de Parto/etiología , Tamaño de los Órganos , Embarazo , Estudios Retrospectivos , Estadística como Asunto , Arterias Umbilicales/patología
4.
Ann Oncol ; 25(7): 1379-1384, 2014 Jul.
Artículo en Inglés | MEDLINE | ID: mdl-24737779

RESUMEN

BACKGROUND: It has not yet been determined whether hepatic arterial infusion (HAI) chemotherapy improves survival in patients with early hepatocellular carcinoma (HCC). We evaluated the effectiveness of HAI with high-concentration cisplatin (DDP-H) for the treatment of HCC by comparing outcomes between patients who received HAI with DDP-H before radical local treatment of early-stage HCC [Japan Integrated Staging (JIS) score 0/1] and patients who did not receive HAI chemotherapy. PATIENTS AND METHODS: Survival was analyzed in 114 patients with early-stage HCC who underwent radical local treatment. The patients were divided into two groups: a HAI group (n = 79) who received DDP-H infusion into the whole liver via the proper hepatic artery, and a non-HAI group (n = 35) who did not receive HAI chemotherapy. RESULTS: The cumulative survival rates at 1, 3, and 5 years were 77.4%, 69.2%, and 55.3% in the non-HAI group and 97.4%, 87.0%, and 84.4% in the HAI group, respectively. Survival time prolonged significantly in the HAI group compared with the non-HAI group (log-rank test: P = 0.023; generalized Wilcoxon test: P = 0.012) Multivariate analysis using the Cox proportional hazards model identified HAI with DDP-H as the most important factor affecting survival. CONCLUSIONS: Whole-liver HAI with DDP-H before radical local treatment can improve the prognosis of patients with early-stage HCC.


Asunto(s)
Antineoplásicos/uso terapéutico , Carcinoma Hepatocelular/tratamiento farmacológico , Cisplatino/uso terapéutico , Neoplasias Hepáticas/tratamiento farmacológico , Tasa de Supervivencia , Antineoplásicos/efectos adversos , Carcinoma Hepatocelular/fisiopatología , Cisplatino/efectos adversos , Humanos , Infusiones Intraarteriales , Neoplasias Hepáticas/fisiopatología , Estudios Prospectivos
5.
Vet J ; 306: 106179, 2024 Jun 14.
Artículo en Inglés | MEDLINE | ID: mdl-38880229

RESUMEN

The potential value of hypervascularity detected with power Doppler ultrasonography (PDU) within equine superficial digital flexor tendon (SDFT) as a prognostic factor of SDFT injury is not clear. The purpose of this study was to test the hypothesis that hypervascularity within SDFT is one of the risk factors for subsequent severe SDFT injury and to evaluate the prognostic value. A prospective cohort study of 97 Thoroughbred racehorses without any clinical signs of SDFT injury was conducted. Six variables of age, body weight, sex, the cross-sectional area of SDFT, PDU signal within SDFT and experience of steeplechase were assessed for the possibility of risk factors of subsequent SDFT injury in follow-up period of 1 year. Multivariable logistic regression analyses were used for assessment of the odds ratios (ORs) and 95 % confidence intervals (CIs) of SDFT injury. Multivariable logistic regression analysis revealed that the PDU signal within SDFT was a risk factor for the development of SDFT injury in follow-up period (P = 0.017). The adjusted OR of SDFT injury was significantly higher in PDU positive group than in PDU negative group (OR 3.17, 95 % CIs 1.20-8.35). Although further studies are required, these results would be useful for early detection and/or prevention of development for clinical severe SDFT injury.

6.
Nat Genet ; 11(2): 207-9, 1995 Oct.
Artículo en Inglés | MEDLINE | ID: mdl-7550352

RESUMEN

A specific isoform of apolipoprotein E has been associated with the accelerated rate of disease expression of sporadic Alzheimer's disease (AD) and late-onset familial AD (FAD). An earlier age at onset has also been demonstrated in familial AD patients with mutations in the amyloid precursor protein (APP) gene (APP717 and APP670/671)13 carrying the APOE epsilon-4 allele compared to those who do not, but not in familial AD patients with APP692 or 693 mutations, or in chromosome 14-linked familial AD patients. Hypothesizing that receptors for apoE-containing lipoproteins act as a potential risk factor for AD, we performed an association study using a polymorphic triplet (CGG) repeat in the gene for the VLDL receptor (VLDL-R), a receptor for apoE-containing lipoproteins. The frequency of the 5-repeat allele was significantly higher in all of the Japanese sporadic AD patients (P < 0.02) than in the Japanese controls. Moreover, the odds ratio was significantly increased in the AD patients homozygous for the 5-repeat allele (OR = 2.1, 95% CI = [1.1-4.2]). Multiple logistic regression analysis reveals that the relative risk conferred by the presence of two copies of the 5-repeat allele and at least one copy of the APOE epsilon-4 allele is 8.7 (95% CI = [2.9-25.8]). Our results suggest that the VLDL-R gene is a susceptibility gene for AD.


Asunto(s)
Enfermedad de Alzheimer/genética , Cromosomas Humanos Par 14 , Receptores de LDL/genética , Secuencias Repetitivas de Ácidos Nucleicos , Alelos , Enfermedad de Alzheimer/epidemiología , Apolipoproteínas E/genética , Secuencia de Bases , Corteza Cerebral/metabolismo , Cartilla de ADN , Humanos , Japón , Datos de Secuencia Molecular , Oportunidad Relativa , Reacción en Cadena de la Polimerasa , Polimorfismo Genético , Valores de Referencia , Análisis de Regresión , Factores de Riesgo
7.
Space Sci Rev ; 218(5): 38, 2022.
Artículo en Inglés | MEDLINE | ID: mdl-35757012

RESUMEN

This paper presents the highlights of joint observations of the inner magnetosphere by the Arase spacecraft, the Van Allen Probes spacecraft, and ground-based experiments integrated into spacecraft programs. The concurrent operation of the two missions in 2017-2019 facilitated the separation of the spatial and temporal structures of dynamic phenomena occurring in the inner magnetosphere. Because the orbital inclination angle of Arase is larger than that of Van Allen Probes, Arase collected observations at higher L -shells up to L ∼ 10 . After March 2017, similar variations in plasma and waves were detected by Van Allen Probes and Arase. We describe plasma wave observations at longitudinally separated locations in space and geomagnetically-conjugate locations in space and on the ground. The results of instrument intercalibrations between the two missions are also presented. Arase continued its normal operation after the scientific operation of Van Allen Probes completed in October 2019. The combined Van Allen Probes (2012-2019) and Arase (2017-present) observations will cover a full solar cycle. This will be the first comprehensive long-term observation of the inner magnetosphere and radiation belts.

8.
Eur Phys J E Soft Matter ; 34(5): 46, 2011 May.
Artículo en Inglés | MEDLINE | ID: mdl-21562968

RESUMEN

We present a Brownian dynamics theory with full hydrodynamics (Stokesian dynamics) for a Gaussian polymer chain embedded in a liquid membrane which is surrounded by bulk solvent and walls. The mobility tensors are derived in Fourier space for the two geometries, namely, a free membrane embedded in a bulk fluid, and a membrane sandwiched by the two walls. Within the preaveraging approximation, a new expression for the diffusion coefficient of the polymer is obtained for the free-membrane geometry. We also carry out a Rouse normal mode analysis to obtain the relaxation time and the dynamical structure factor. For large polymer size, both quantities show Zimm-like behavior in the free-membrane case, whereas they are Rouse-like for the sandwiched membrane geometry. We use the scaling argument to discuss the effect of excluded-volume interactions on the polymer relaxation time.


Asunto(s)
Proteínas de la Membrana/química , Simulación de Dinámica Molecular , Polímeros/química , Difusión , Hidrodinámica , Proteínas de la Membrana/metabolismo , Tamaño de la Partícula , Polímeros/metabolismo , Solventes/química
9.
Nature ; 436(7051): 655-9, 2005 Aug 04.
Artículo en Inglés | MEDLINE | ID: mdl-16079836

RESUMEN

The nitrogen in lunar soils is correlated to the surface and therefore clearly implanted from outside. The straightforward interpretation is that the nitrogen is implanted by the solar wind, but this explanation has difficulties accounting for both the abundance of nitrogen and a variation of the order of 30 per cent in the 15N/14N ratio. Here we propose that most of the nitrogen and some of the other volatile elements in lunar soils may actually have come from the Earth's atmosphere rather than the solar wind. We infer that this hypothesis is quantitatively reasonable if the escape of atmospheric gases, and implantation into lunar soil grains, occurred at a time when the Earth had essentially no geomagnetic field. Thus, evidence preserved in lunar soils might be useful in constraining when the geomagnetic field first appeared. This hypothesis could be tested by examination of lunar farside soils, which should lack the terrestrial component.


Asunto(s)
Planeta Tierra , Medio Ambiente Extraterrestre/química , Sedimentos Geológicos/química , Modelos Teóricos , Luna , Nitrógeno/análisis , Gases Nobles/análisis , Atmósfera/química , Historia Antigua , Iones/análisis , Magnetismo , Isótopos de Nitrógeno , Viento
10.
J Exp Med ; 171(2): 577-82, 1990 Feb 01.
Artículo en Inglés | MEDLINE | ID: mdl-2303787

RESUMEN

Mixed isotype A beta dE alpha d class II molecule-restricted antigen-reactive T cell clones were obtained from (BALB/c x B6E alpha d)F1 mice. These T cell clones responded to keyhole limpet hemocyanin in the presence of (BALB/c x B6E alpha d)F1 but not CBF1 APCs. Both anti-A beta d and anti-E alpha mAbs blocked the proliferative responses of these clones. The frequency of such mixed isotype A beta E alpha-restricted T cell clones in (BALB/c x B6E alpha d)F1 mice was estimated to be approximately 10% from our limiting dilution cloning. The existence of such mixed isotype class II molecule-restricted T cells would have important implications for the expansion of the T cell repertoire as well as the induction of autoimmunity.


Asunto(s)
Antígenos CD4/inmunología , Linfocitos T/inmunología , Animales , Células Clonales , Ratones , Ratones Transgénicos
11.
Phys Rev Lett ; 105(4): 046103, 2010 Jul 23.
Artículo en Inglés | MEDLINE | ID: mdl-20867867

RESUMEN

The correlation between the geometric and electronic structures of Zn-phthalocyanine (ZnPc) and F16ZnPc on Cu(111) were studied by x-ray standing wave and angle-resolved photoemission spectroscopy. We found evidence for a distortion of the planar molecules upon adsorption, with the central Zn atom in the molecule protruding towards the substrate. This modifies the energy levels of both the molecule and the substrate, which appear as interface states. The site-specific geometric and electronic relaxations are an important effect for organic-metal interface energetics.

12.
J Evol Biol ; 23(11): 2377-84, 2010 Nov.
Artículo en Inglés | MEDLINE | ID: mdl-20825549

RESUMEN

Development is left-right reversed between dextral and sinistral morphs of snails. In sympatry, they share the same gene pool, including polygenes for shell shape. Nevertheless, their shell shapes are not the mirror images of each other. This triggered a debate between hypotheses that argue either for a developmental constraint or for zygotic pleiotropic effects of the polarity gene. We found that dextrals can be wider or narrower than sinistrals depending on the population, contrary to the prediction of invariable deviation under a developmental constraint. If the pleiotropy is solely responsible instead, the mean shape of each morph should change, depending on the frequency of polarity genotype. Our simulations of this mean shape change under zygotic pleiotropy, however, show that the direction of interchiral difference remains the same regardless of genotype frequency. Our results suggest the presence of genetic variation among populations that changes the maternal or zygotic pleiotropic effect of the polarity gene.


Asunto(s)
Estructuras Animales/anatomía & histología , Tipificación del Cuerpo/fisiología , Pleiotropía Genética/fisiología , Patrón de Herencia/genética , Caracoles/anatomía & histología , Animales , Pesos y Medidas Corporales , Análisis Multivariante , Tailandia
13.
Eur Phys J E Soft Matter ; 31(3): 303-10, 2010 Mar.
Artículo en Inglés | MEDLINE | ID: mdl-20306216

RESUMEN

Using a hydrodynamic theory that incorporates a momentum decay mechanism, we calculate the drag coefficient of a circular liquid domain of finite viscosity moving in a two-dimensional membrane. We derive an analytical expression for the drag coefficient which covers the whole range of domain sizes. Several limiting expressions are discussed. The obtained drag coefficient decreases as the domain viscosity becomes smaller with respect to the outer membrane viscosity. This is because the flow induced in the domain acts to transport the fluid in the surrounding matrix more efficiently.


Asunto(s)
Membrana Celular/química , Aire , Lípidos/química , Viscosidad , Agua/química
14.
Ann Oncol ; 20(1): 71-7, 2009 Jan.
Artículo en Inglés | MEDLINE | ID: mdl-18723551

RESUMEN

BACKGROUND: The current study examined the clinical usefulness of YKL-40 in detection and prognosis of uterine cervical cancer. PATIENTS AND METHODS: Serum levels of YKL-40, cancer antigen 125 (CA 125), carbohydrate antigen 19-9 (CA19-9), and squamous cell carcinoma (SCC) antigen were determined by enzyme-linked immunosorbent assay in women with benign gynecologic disease (n=24), cervical malignancy (SCC, n=104; adenocarcinoma, n=37), and age-matched healthy controls (n=45). Immunohistochemical analysis for local YKL-40 expression was carried out on 28 adenocarcinomas. RESULTS: Receiver operating characteristic curve analysis showed that YKL-40 [area under the curve (AUC)=0.882] was significantly better at discriminating adenocarcinoma from healthy control than SCC antigen, CA 125, and CA19-9. For SCC, YKL-40 (AUC=0.898) carried out similarly to SCC antigen and was better than CA 125 and CA19-9. Using a cut-off YKL-40 value of 92.2 ng/ml, sensitivity of YKL-40 in stage I adenocarcinoma (68%) was higher than that of the other three markers (11%-21%). Tumor-associated macrophages showed immunoreactivity for YKL-40 in 2 of 28 adenocarcinoma tissue samples, but adenocarcinoma cells themselves were nonimmunoreactive in all samples. Multivariate Cox regression analysis revealed that elevated pretreatment YKL-40 levels predicted unfavorable prognosis, independent of International Federation of Gynecology and Obstetrics stage and age at diagnosis. CONCLUSIONS: Pretreatment serum YKL-40 level is a possible prognosticator of cervical adenocarcinoma.


Asunto(s)
Adenocarcinoma/diagnóstico , Biomarcadores de Tumor/sangre , Glicoproteínas/sangre , Neoplasias del Cuello Uterino/diagnóstico , Adenocarcinoma/sangre , Adenocarcinoma/metabolismo , Adipoquinas , Adulto , Anciano , Anciano de 80 o más Años , Biomarcadores de Tumor/metabolismo , Carcinoma de Células Escamosas/sangre , Carcinoma de Células Escamosas/diagnóstico , Carcinoma de Células Escamosas/metabolismo , Estudios de Casos y Controles , Proteína 1 Similar a Quitinasa-3 , Femenino , Glicoproteínas/metabolismo , Glicoproteínas/normas , Humanos , Lectinas , Persona de Mediana Edad , Pronóstico , Valores de Referencia , Sensibilidad y Especificidad , Neoplasias del Cuello Uterino/sangre , Neoplasias del Cuello Uterino/metabolismo
15.
Science ; 291(5510): 1939-41, 2001 Mar 09.
Artículo en Inglés | MEDLINE | ID: mdl-11239148

RESUMEN

In Earth's environment, the observed polar outflow rate for O(+) ions, the main source of oxygen above gravitational escape energy, corresponds to the loss of approximately 18% of the present-day atmospheric oxygen over 3 billion years. However, part of this apparent loss can actually be returned to the atmosphere. Examining loss rates of four escape routes with high-altitude spacecraft observations, we show that the total oxygen loss rate inferred from current knowledge is about one order of magnitude smaller than the polar O(+) outflow rate. This disagreement suggests that there may be a substantial return flux from the magnetosphere to the low-latitude ionosphere. Then the net oxygen loss over 3 billion years drops to approximately 2% of the current atmospheric oxygen content.

16.
Kyobu Geka ; 62(13): 1182-5, 2009 Dec.
Artículo en Japonés | MEDLINE | ID: mdl-19999100

RESUMEN

Clear cell adenocarcinoma with endobronchial polypoid growth of the lung is extremely rare. A 65-year-old male with hemosputum was found to have an abnormal shadow in the hilum of the left lung. Computed tomography of the chest revealed that a heterogeneous mass occupied the lumen extending outside the upper lobe bronchus of the left lung. By biopsy, the tumor was determined to be adenocarcinoma. The patient underwent left pneumonectomy with mediastinal lymph node dissection. Macroscopically, the tumor showed a polypoid growth along with the bronchial tree. Microscopically, most of the tumor was composed of large clear cells with partial glandular formation, indicating the tumor to be adenocarcinoma Lymph node metastasis was seen in #5 and #12u. The lung cancer was diagnosed as clear cell adenocarcinoma with endobronchial polypoid growth.


Asunto(s)
Adenocarcinoma de Células Claras/patología , Bronquios/patología , Neoplasias Pulmonares/patología , Pólipos/patología , Anciano , Humanos , Masculino
17.
Space Sci Rev ; 215(1): 9, 2019.
Artículo en Inglés | MEDLINE | ID: mdl-30880847

RESUMEN

With the advent of the Heliophysics/Geospace System Observatory (H/GSO), a complement of multi-spacecraft missions and ground-based observatories to study the space environment, data retrieval, analysis, and visualization of space physics data can be daunting. The Space Physics Environment Data Analysis System (SPEDAS), a grass-roots software development platform (www.spedas.org), is now officially supported by NASA Heliophysics as part of its data environment infrastructure. It serves more than a dozen space missions and ground observatories and can integrate the full complement of past and upcoming space physics missions with minimal resources, following clear, simple, and well-proven guidelines. Free, modular and configurable to the needs of individual missions, it works in both command-line (ideal for experienced users) and Graphical User Interface (GUI) mode (reducing the learning curve for first-time users). Both options have "crib-sheets," user-command sequences in ASCII format that can facilitate record-and-repeat actions, especially for complex operations and plotting. Crib-sheets enhance scientific interactions, as users can move rapidly and accurately from exchanges of technical information on data processing to efficient discussions regarding data interpretation and science. SPEDAS can readily query and ingest all International Solar Terrestrial Physics (ISTP)-compatible products from the Space Physics Data Facility (SPDF), enabling access to a vast collection of historic and current mission data. The planned incorporation of Heliophysics Application Programmer's Interface (HAPI) standards will facilitate data ingestion from distributed datasets that adhere to these standards. Although SPEDAS is currently Interactive Data Language (IDL)-based (and interfaces to Java-based tools such as Autoplot), efforts are under-way to expand it further to work with python (first as an interface tool and potentially even receiving an under-the-hood replacement). We review the SPEDAS development history, goals, and current implementation. We explain its "modes of use" with examples geared for users and outline its technical implementation and requirements with software developers in mind. We also describe SPEDAS personnel and software management, interfaces with other organizations, resources and support structure available to the community, and future development plans. ELECTRONIC SUPPLEMENTARY MATERIAL: The online version of this article (10.1007/s11214-018-0576-4) contains supplementary material, which is available to authorized users.

18.
J Phys Chem B ; 112(19): 6107-13, 2008 May 15.
Artículo en Inglés | MEDLINE | ID: mdl-18179196

RESUMEN

Barrierless chemical reactions have often been modeled as a Brownian motion on a one-dimensional harmonic potential energy surface with a position-dependent reaction sink or window located near the minimum of the surface. This simple (but highly successful) description leads to a nonexponential survival probability only at small to intermediate times but exponential decay in the long-time limit. However, in several reactive events involving proteins and glasses, the reactions are found to exhibit a strongly nonexponential (power law) decay kinetics even in the long time. In order to address such reactions, here, we introduce a model of barrierless chemical reaction where the motion along the reaction coordinate sustains dispersive diffusion. A complete analytical solution of the model can be obtained only in the frequency domain, but an asymptotic solution is obtained in the limit of long time. In this case, the asymptotic long-time decay of the survival probability is a power law of the Mittag-Leffler functional form. When the barrier height is increased, the decay of the survival probability still remains nonexponential, in contrast to the ordinary Brownian motion case where the rate is given by the Smoluchowski limit of the well-known Kramers' expression. Interestingly, the reaction under dispersive diffusion is shown to exhibit strong dependence on the initial state of the system, thus predicting a strong dependence on the excitation wavelength for photoisomerization reactions in a dispersive medium. The theory also predicts a fractional viscosity dependence of the rate, which is often observed in the reactions occurring in complex environments.


Asunto(s)
Tampones (Química) , Difusión , Probabilidad
19.
J Chem Phys ; 129(22): 224507, 2008 Dec 14.
Artículo en Inglés | MEDLINE | ID: mdl-19071928

RESUMEN

Soft x-ray emission spectroscopy was used for elucidating the electronic structure of ionic liquids [C(4)mim](+)PF(6)(-) and [C(4)mim](+)OTf(-), where [C(4)mim](+) stands for methylbutylimidazolium cation and OTf(-) for the trifluoromethanesulfonate anion. Nonresonant spectra measured above N, O, and F 1s edges selectively probed the molecular orbitals (MOs) of the cation and anions. They give a clear evidence that the highest occupied molecular orbital of the [C(4)mim](+) cation contributes to the topmost occupied states of the ionic liquids [C(4)mim](+)PF(6)(-), while both cationic and anionic MOs contribute for the case of [C(4)mim](+)OTf(-). Resonant soft x-ray emission spectra at the N 1s edge of these ionic liquids revealed that the energy gap of [C(4)mim](+)PF(6)(-) is solely determined by the [C(4)mim](+) cation, in contrast to usual ionic crystals. The ionic liquids form a new class of the ionic materials from the viewpoint of the electronic structure.

20.
Phys Rev E Stat Nonlin Soft Matter Phys ; 77(3 Pt 1): 031505, 2008 Mar.
Artículo en Inglés | MEDLINE | ID: mdl-18517386

RESUMEN

The Ivanov-Anderson model (and an earlier treatment by Kubo) envisages a decay of the orientational correlation by random but large amplitude molecular jumps, as opposed to infinitesimal small jumps assumed in Brownian diffusion. Recent computer simulation studies on water and viscous liquids have shown that large amplitude motions may indeed be more of a rule than exception. Existing theoretical studies on jump diffusion mostly assume an exponential (Poissonian) waiting time distribution for jumps, thereby again leading to an exponential decay. Here we extend the existing formalism of Ivanov and Anderson to include an algebraic waiting time distribution between two jumps. As a result, the first (l=1) and second (l=2) rank orientational time correlation functions show the same long time power law, but their short time decay behavior is quite different. The predicted Cole-Cole plot of dielectric relaxation reproduces various features of non-Debye behavior observed experimentally. We also developed a theory where both unrestricted small jumps and large angular jumps coexist simultaneously. The small jumps are shown to have a large effect on the long time decay, particularly in mitigating the effects of algebraic waiting time distribution, and in giving rise to an exponential-like decay, with a time constant, surprisingly, less than the time constant that arises from small amplitude decay alone.

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