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1.
Prehosp Emerg Care ; 27(5): 695-703, 2023.
Artigo em Inglês | MEDLINE | ID: mdl-35543652

RESUMO

OBJECTIVES: Early airway management during cardiopulmonary resuscitation (CPR) prevents aspiration of gastric contents. Endotracheal intubation is the gold standard to protect airways, but supraglottic airway devices (SGA) may provide some protection with less training. Bag-mask ventilation (BMV) is the most common method used by rescuers. We hypothesized that SGA use by first rescuers during CPR could increase ventilation success rate and also decrease intragastric pressure and pulmonary aspiration. METHODS: We performed a randomized cross-over experimental trial on human cadavers. Protocol A: we assessed the rate of successful ventilation (chest rise), intragastric pressure, and CPR key time metrics. Protocol B: cadaver stomachs were randomized to be filled with 300 mL of either blue or green serum saline solution through a Foley catheter. Each rescuer was randomly assigned to use SGA or BMV during a 5-minute standard CPR period. Then, in a crossover design, the stomach was filled with the second color solution and another 5-minute CPR period was performed using the other airway method. Pulmonary aspiration, defined as the presence of colored solution below the vocal cords, was assessed by a blinded operator using bronchoscopy. A generalized linear mixed model was used for statistical analysis. RESULTS: Protocol A: Forty-eight rescuers performed CPR on 11 cadavers. Median ventilation success was higher with SGA than BMV: 75.0% (IQR: 59.8-87.3) vs. 34.7% (IQR: 25.0-50.0), (p = 0.003). Gastric pressure and differential (maximum minus minimum) gastric pressure were lower in the SGA group: 2.21 mmHg (IQR: 1.66; 2.68) vs. 3.02 mmHg (IQR: 2.02; 4.22) (p = 0.02) and 5.70 mmHg (IQR: 4.10; 7.60) vs. 8.05 mmHg (IQR: 5.40; 11.60) (p = 0.05). CPR key times were not different between groups. Protocol B: Ten cadavers were included with 20 CPR periods. Aspiration occurred in 2 (20%) SGA procedures and 5 (50%) BMV procedures (p = 0.44). CONCLUSION: Use of SGA by rescuers improved the ventilation success rate, decreased intragastric pressure, and did not affect key CPR metrics. SGA use by basic life support rescuers appears feasible and efficient.


Assuntos
Reanimação Cardiopulmonar , Serviços Médicos de Emergência , Humanos , Reanimação Cardiopulmonar/métodos , Estudos Cross-Over , Intubação Intratraqueal/métodos , Cadáver
2.
J Chem Phys ; 157(24): 244504, 2022 Dec 28.
Artigo em Inglês | MEDLINE | ID: mdl-36586975

RESUMO

We investigate the structural relaxation of a soft-sphere liquid quenched isochorically (ϕ = 0.7) and instantaneously to different temperatures Tf above and below the glass transition. For this, we combine extensive Brownian dynamics simulations and theoretical calculations based on the non-equilibrium self-consistent generalized Langevin equation (NE-SCGLE) theory. The response of the liquid to a quench generally consists of a sub-linear increase of the α-relaxation time with system's age. Approaching the ideal glass-transition temperature from above (Tf > Ta), sub-aging appears as a transient process describing a broad equilibration crossover for quenches to nearly arrested states. This allows us to empirically determine an equilibration timescale teq(Tf) that becomes increasingly longer as Tf approaches Ta. For quenches inside the glass (Tf ≤ Ta), the growth rate of the structural relaxation time becomes progressively larger as Tf decreases and, unlike the equilibration scenario, τα remains evolving within the whole observation time-window. These features are consistently found in theory and simulations with remarkable semi-quantitative agreement and coincide with those revealed in a previous and complementary study [P. Mendoza-Méndez et al., Phys. Rev. 96, 022608 (2017)] that considered a sequence of quenches with fixed final temperature Tf = 0 but increasing ϕ toward the hard-sphere dynamical arrest volume fraction ϕHS a=0.582. The NE-SCGLE analysis, however, unveils various fundamental aspects of the glass transition, involving the abrupt passage from the ordinary equilibration scenario to the persistent aging effects that are characteristic of glass-forming liquids. The theory also explains that, within the time window of any experimental observation, this can only be observed as a continuous crossover.


Assuntos
Vidro , Simulação de Dinâmica Molecular , Temperatura , Temperatura de Transição , Vidro/química
3.
Phys Rev E ; 100(4-1): 042601, 2019 Oct.
Artigo em Inglês | MEDLINE | ID: mdl-31770981

RESUMO

We contrast the generic features of structural relaxation close to the idealized glass transition that are predicted by the self-consistent generalized Langevin equation theory (SCGLE) against those that are predicted by the mode-coupling theory of the glass transition (MCT). We present an asymptotic solution close to conditions of kinetic arrest that is valid for both theories, despite the different starting points that are adopted in deriving them. This in particular provides the same level of understanding of the asymptotic dynamics in the SCGLE as was previously done only for MCT. We discuss similarities and different predictions of the two theories for kinetic arrest in standard glass-forming models, as exemplified through the hard-sphere system. Qualitative differences are found for models where a decoupling of relaxation modes is predicted, such as the generalized Gaussian core model, or binary hard-sphere mixtures of particles with very disparate sizes. These differences, which arise in the distinct treatment of the memory kernels associated to self- and collective motion of particles, lead to distinct scenarios that are predicted by each theory for partially arrested states and in the vicinity of higher-order glass-transition singularities.

4.
Rev. esp. anestesiol. reanim ; 66(6): 299-306, jun.-jul. 2019. tab, graf
Artigo em Espanhol | IBECS | ID: ibc-187538

RESUMO

Objetivo: La isquemia derivada de la aplicación del torniquete es un factor fibrinolítico que podría potenciar la eficacia del ácido tranexámico (ATx) en artroplastia total de rodilla (ATR) frente a la artroplastia total de cadera (ATC). Nuestro objetivo es comparar el efecto del ATx sobre sangrado y fibrinólisis en estas 2 artroplastias, valorando la incidencia de complicaciones. Método: Ensayo clínico prospectivo, aleatorizado y doble ciego. Los pacientes programados para ATR o ATC recibían ATx (2 infusiones 10mg/kg) o placebo. Se cuantificó sangrado y parámetros de fibrinólisis, y se detectaron complicaciones tromboembólicas con ecografía doppler y tomografía computarizada. Resultados: Fueron incluidos 44 pacientes (11 ATC y 11 ATR tratados con ATx; 11 ATC y 11 ATR fueron controles). El sangrado fue significativamente menor en el grupo tratado con ATx (promedio 921mL vs. 1383mL en ATC y 969mL vs. 1223mL en ATR) y se necesitaron menos transfusiones (ninguna frente a 5 unidades en grupo control). El ATx fue igualmente eficaz en la reducción del sangrado en ambas cirugías (reducción del 33% en ATC y del 21% en ATR). El gran incremento medio de dímero D entre el periodo basal y las 6h (1.004 a 10.284μg /L en ATC y 571 a 6.480μg /L en ATR) es atenuado por el uso de ATx (1.077 a 2.590μg/L en ATC y 655 a 2.535μg/L en ATR). No hubo diferencias significativas en eventos tromboembólicos. Conclusiones: El ATx profiláctico es igualmente efectivo en ATR y ATC para reducir sangrado. Ambas cirugías tienen efecto similar sobre la fibrinólisis


Background: Tourniquet-induced ischaemia could increase fibrinolysis and enhance tranexamic acid (TXA) efficacy in total knee arthroplasty (TKA) compared to total hip arthroplasty (THA). The aims of this study are to compare the effect of TXA on bleeding and fibrinolysis in both types of surgery, and to record thromboembolic complications. Methods: A prospective double-blind study was conducted on patients scheduled for TKA or THA who received TXA (2 bolus of 10mg/kg) or placebo. Bleeding and fibrinolysis were evaluated. Doppler-ultrasound and computed tomography were performed in order to assess any thromboembolic complications. Results: A total of 44 patients were included (11 THA and 11 TKA treated with TXA; 11 THA and 11 TKA as controls). Blood losses were significantly lower in the TXA group (mean 921mL vs 1,383mL in THA and 969mL vs 1,223mL in TKA), and no transfusions were needed with TXA, whereas 5 blood units were transfused in controls. TXA was equally effecting in reducing bleeding in both surgeries (33% in THA and 21% in TKA). The significant mean increase in D-dimers from baseline to 6 hours after surgery (1,004 ug/L to 10,284 ug/L in THA and 571 ug/L to 6,480 ug/L in TKA) was attenuated by TXA (1,077 ug/L to 2,590 ug/L in THA and 655 ug/L to 2,535 ug/L in TKA). There were no differences in thromboembolic episodes. Conclusions: Prophylactic use of tranexamic acid is equally effective in reducing bleeding in TKA and THA. Both surgeries have a similar effect on fibrinolysis


Assuntos
Humanos , Masculino , Feminino , Pessoa de Meia-Idade , Idoso , Ácido Tranexâmico/farmacocinética , Perda Sanguínea Cirúrgica/prevenção & controle , Fibrinólise/efeitos dos fármacos , Artroplastia de Quadril/estatística & dados numéricos , Artroplastia do Joelho/estatística & dados numéricos , Estudos Prospectivos , Método Duplo-Cego , Tromboembolia/diagnóstico por imagem , Transfusão de Sangue/estatística & dados numéricos , Pré-Medicação/estatística & dados numéricos , Estudos de Casos e Controles
5.
Artigo em Inglês, Espanhol | MEDLINE | ID: mdl-30902396

RESUMO

BACKGROUND: Tourniquet-induced ischaemia could increase fibrinolysis and enhance tranexamic acid (TXA) efficacy in total knee arthroplasty (TKA) compared to total hip arthroplasty (THA). The aims of this study are to compare the effect of TXA on bleeding and fibrinolysis in both types of surgery, and to record thromboembolic complications. METHODS: A prospective double-blind study was conducted on patients scheduled for TKA or THA who received TXA (2 bolus of 10mg/kg) or placebo. Bleeding and fibrinolysis were evaluated. Doppler-ultrasound and computed tomography were performed in order to assess any thromboembolic complications. RESULTS: A total of 44 patients were included (11 THA and 11 TKA treated with TXA; 11 THA and 11 TKA as controls). Blood losses were significantly lower in the TXA group (mean 921mL vs 1,383mL in THA and 969mL vs 1,223mL in TKA), and no transfusions were needed with TXA, whereas 5 blood units were transfused in controls. TXA was equally effecting in reducing bleeding in both surgeries (33% in THA and 21% in TKA). The significant mean increase in D-dimers from baseline to 6 hours after surgery (1,004 ug/L to 10,284 ug/L in THA and 571 ug/L to 6,480 ug/L in TKA) was attenuated by TXA (1,077 ug/L to 2,590 ug/L in THA and 655 ug/L to 2,535 ug/L in TKA). There were no differences in thromboembolic episodes. CONCLUSIONS: Prophylactic use of tranexamic acid is equally effective in reducing bleeding in TKA and THA. Both surgeries have a similar effect on fibrinolysis.


Assuntos
Antifibrinolíticos/uso terapêutico , Artroplastia de Quadril , Artroplastia do Joelho , Perda Sanguínea Cirúrgica/prevenção & controle , Fibrinólise/efeitos dos fármacos , Ácido Tranexâmico/uso terapêutico , Idoso , Idoso de 80 Anos ou mais , Antifibrinolíticos/farmacologia , Método Duplo-Cego , Feminino , Humanos , Masculino , Pessoa de Meia-Idade , Estudos Prospectivos , Ácido Tranexâmico/farmacologia
6.
Talanta ; 178: 178-187, 2018 Feb 01.
Artigo em Inglês | MEDLINE | ID: mdl-29136810

RESUMO

An electronic tongue (ET) consisting of two voltammetric sensors, namely a poly-ethylendioxythiophene modified Pt electrode and a sonogel carbon electrode, has been developed aiming at monitoring grape ripening. To test the effectiveness of device and measurement procedures developed, samples of three varieties of grapes have been collected from veraison to harvest of the mature grape bunches. The derived musts have been then submitted to electrochemical investigation using Differential Pulse Voltammetry technique. At the same time, quantitative determination of specific analytical parameters for the evaluation of technological and phenolic maturity of each sample has been performed by means of conventional analytical techniques. After a preliminary inspection by principal component analysis, calibration models were calculated both by partial least squares (PLS) on the whole signals and by the interval partial least squares (iPLS) variable selection algorithm, in order to estimate physico-chemical parameters. Calibration models have been obtained both considering separately the signals of each sensor of the ET, and by proper fusion of the voltammetric data selected from the two sensors by iPLS. The latter procedure allowed us to check the possible complementarity of the information brought by the different electrodes. Good predictive models have been obtained for estimation of pH, total acidity, sugar content, and anthocyanins content. The application of the ET for fast evaluation of grape ripening and of most suitable harvesting time is proposed.


Assuntos
Nariz Eletrônico , Vitis/química , Vitis/crescimento & desenvolvimento , Compostos Bicíclicos Heterocíclicos com Pontes/química , Calibragem , Eletrodos , Concentração de Íons de Hidrogênio , Análise dos Mínimos Quadrados , Análise Multivariada , Polímeros/química , Vinho/análise
7.
Rev. esp. anestesiol. reanim ; 64(3): 172-176, mar. 2017. tab, ilus
Artigo em Espanhol | IBECS | ID: ibc-159956

RESUMO

Se describe el caso de un paciente de 19 años que ingresó en Urgencias de nuestro hospital con un cuadro de movimientos disautonómicos y desconexión del medio tras ingesta de anfetamina 4 días antes, evolucionando a un síndrome catatónico y finalmente a estatus epiléptico. El diagnóstico definitivo fue encefalitis por anticuerpos antirreceptores de NMDA, una inflamación límbica aguda de origen autoinmune en la que el diagnóstico y el tratamiento tempranos son clave en el pronóstico. En el caso descrito, las pruebas iniciales normales y el antecedente de intoxicación por metanfetamina hicieron que el diagnóstico se viera retrasado, pues la intoxicación por metanfetamina inhalada produce una clínica similar. Adicionalmente, esta intoxicación podría haber producido un estado inmunitario sobre el paciente y favorecer el desarrollo de la enfermedad (AU)


A 19-year-old male came to the Emergency Room of our hospital due to an episode of dystonic movements and disorientation 4 days after consuming methamphetamine, which evolved to a catatonic frank syndrome and eventually to status epilepticus. Definitive diagnosis was anti-NMDA receptor encephalitis, an acute inflammation of the limbic area of autoimmune origin in which early diagnosis and treatment are key elements for the final outcome. In this case, initial normal tests and previous methamphetamine poisoning delayed diagnosis, because inhaled-methamphetamine poisoning causes similar clinical symptoms to anti-NMDA receptor encephalitis. Methamphetamine poisoning may have caused an immune response in the patient, bringing on the progress of the pathology (AU)


Assuntos
Humanos , Masculino , Adulto , Encefalite Antirreceptor de N-Metil-D-Aspartato/complicações , Encefalite Antirreceptor de N-Metil-D-Aspartato/tratamento farmacológico , Encefalite Antirreceptor de N-Metil-D-Aspartato , Diagnóstico Diferencial , Encefalite Límbica/induzido quimicamente , Encefalite Límbica/complicações , Transtornos Paranoides/induzido quimicamente , Transtornos Paranoides/complicações , Doenças do Sistema Nervoso/complicações , Doenças do Sistema Nervoso/tratamento farmacológico , Neuroimunomodulação , Metanfetamina/efeitos adversos , Metanfetamina/toxicidade , Biomarcadores Tumorais/análise , Eletroencefalografia , Eletroencefalografia/métodos
8.
Rev Esp Anestesiol Reanim ; 64(3): 172-176, 2017 Mar.
Artigo em Inglês, Espanhol | MEDLINE | ID: mdl-27919412

RESUMO

A 19-year-old male came to the Emergency Room of our hospital due to an episode of dystonic movements and disorientation 4 days after consuming methamphetamine, which evolved to a catatonic frank syndrome and eventually to status epilepticus. Definitive diagnosis was anti-NMDA receptor encephalitis, an acute inflammation of the limbic area of autoimmune origin in which early diagnosis and treatment are key elements for the final outcome. In this case, initial normal tests and previous methamphetamine poisoning delayed diagnosis, because inhaled-methamphetamine poisoning causes similar clinical symptoms to anti-NMDA receptor encephalitis. Methamphetamine poisoning may have caused an immune response in the patient, bringing on the progress of the pathology.


Assuntos
Encefalite Antirreceptor de N-Metil-D-Aspartato/diagnóstico , Metanfetamina/envenenamento , Encefalite Antirreceptor de N-Metil-D-Aspartato/etiologia , Encefalite Antirreceptor de N-Metil-D-Aspartato/imunologia , Anticonvulsivantes/uso terapêutico , Autoanticorpos/líquido cefalorraquidiano , Benzodiazepinas/uso terapêutico , Catatonia/etiologia , Catatonia/terapia , Diagnóstico Tardio , Diagnóstico Diferencial , Erros de Diagnóstico , Diazepam/uso terapêutico , Eletroconvulsoterapia , Emergências , Epilepsias Parciais/induzido quimicamente , Epilepsias Parciais/diagnóstico , Alucinações/tratamento farmacológico , Alucinações/etiologia , Humanos , Encefalite Infecciosa/diagnóstico , Masculino , Olanzapina , Intoxicação/diagnóstico , Intoxicação/imunologia , Receptores de N-Metil-D-Aspartato/imunologia , Estado Epiléptico/tratamento farmacológico , Estado Epiléptico/etiologia , Adulto Jovem
9.
J Phys Chem B ; 120(32): 7975-87, 2016 08 18.
Artigo em Inglês | MEDLINE | ID: mdl-27461585

RESUMO

The nonequilibrium self-consistent generalized Langevin equation theory of irreversible processes in liquids is extended to describe the positional and orientational thermal fluctuations of the instantaneous local concentration profile n(r,Ω,t) of a suddenly quenched colloidal liquid of particles interacting through nonspherically symmetric pairwise interactions, whose mean value n(r,Ω,t) is constrained to remain uniform and isotropic, n (r,Ω, t) = n (t). Such self-consistent theory is cast in terms of the time-evolution equation of the covariance [Formula: see text] of the fluctuations [Formula: see text] of the spherical harmonics projections nlm(k;t) of the Fourier transform of n(r,Ω,t). The resulting theory describes the nonequilibrium evolution after a sudden temperature quench of both, the static structure factor projections Slm(k,t) and the two-time correlation function [Formula: see text], where τ is the correlation delay time and t is the evolution or waiting time after the quench. As a concrete and illustrative application we use the resulting self-consistent equations to describe the irreversible processes of equilibration or aging of the orientational degrees of freedom of a system of strongly interacting classical dipoles with quenched positional disorder.

10.
Arch. Soc. Esp. Oftalmol ; 90(1): 26-29, ene. 2015. ilus
Artigo em Espanhol | IBECS | ID: ibc-136348

RESUMO

CASO CLÍNICO: Se presenta el caso clínico de un varón de 63 años con una atrofia macular en el curso de un síndrome de Terson. El paciente mostraba una disminución de la agudeza visual con adelgazamiento macular observado en la tomografía óptica de coherencia. DISCUSIÓN: El paciente presentó una atrofia macular probablemente secundaria a una hemorragia en polo posterior, tras síndrome de Terson causado por la rotura de un aneurisma cerebral


CASE REPORT: The case is presented on a 63-year-old patient with Terson's syndrome who complained of loss of visual acuity. The optical coherence tomography showed macular atrophy. DISCUSSION: The patient developed macular atrophy probably secondary to macular hemorrhage caused by the rupture of a cerebral aneurysm


Assuntos
Humanos , Masculino , Atrofia Muscular/congênito , Atrofia Muscular/patologia , Hemorragia/sangue , Aneurisma Intracraniano/metabolismo , Aneurisma Intracraniano/cirurgia , Vasos Retinianos/anormalidades , Vasos Retinianos/citologia , Esclerose Múltipla/metabolismo , Atrofia Muscular/complicações , Atrofia Muscular/genética , Atrofia Muscular/cirurgia , Hemorragia/complicações , Aneurisma Intracraniano/complicações , Aneurisma Intracraniano/diagnóstico , Vasos Retinianos/lesões , Vasos Retinianos/transplante , Esclerose Múltipla/diagnóstico
11.
Food Chem ; 168: 218-24, 2015 Feb 01.
Artigo em Inglês | MEDLINE | ID: mdl-25172703

RESUMO

Winemaking of musts acidified with up to 3g/L of gypsum (CaSO4 2H2O) and tartaric acid, both individually and in combination, as well as a chemical modeling have been carried out to study the behaviour of these compounds as acidifiers. Prior to fermentation gypsum and tartaric acid reduce the pH by 0.12 and 0.17 pH units/g/L, respectively, but while gypsum does not increase the total acidity and reduces buffering power, tartaric acid shows the opposite behaviour. When these compounds were used in combination, the doses of tartaric acid necessary to reach a suitable pH were reduced. Calcium concentrations increase considerably in gypsum-acidified must, although they fell markedly after fermentation over time. Sulfate concentrations also increased, although with doses of 2g/L they were lower than the maximum permitted level (2.5g/L). Chemical modeling gave good results and the errors in pH predictions were less than 5% in almost all cases.


Assuntos
Sulfato de Cálcio/química , Tartaratos/química , Vitis/química , Fermentação , Concentração de Íons de Hidrogênio , Modelos Químicos , Vinho/análise
12.
Arch Soc Esp Oftalmol ; 90(1): 26-9, 2015 Jan.
Artigo em Espanhol | MEDLINE | ID: mdl-25443182

RESUMO

CASE REPORT: The case is presented on a 63-year-old patient with Terson's syndrome who complained of loss of visual acuity. The optical coherence tomography showed macular atrophy. DISCUSSION: The patient developed macular atrophy probably secondary to macular hemorrhage caused by the rupture of a cerebral aneurysm.


Assuntos
Aneurisma Roto/complicações , Aneurisma Intracraniano/complicações , Macula Lutea/patologia , Hemorragia Vítrea/etiologia , Atrofia , Angiofluoresceinografia , Humanos , Masculino , Pessoa de Meia-Idade , Hemorragia Subaracnóidea/etiologia , Síndrome , Tomografia de Coerência Óptica
13.
Curr Top Med Chem ; 14(23): 2684-93, 2014.
Artigo em Inglês | MEDLINE | ID: mdl-25515750

RESUMO

Choline kinase (CK) is a homodimeric enzyme that catalyses the transfer of the ATP γ-phosphate to choline, generating phosphocholine and ADP in the presence of magnesium. Several isoforms of CK are present in humans but only the HsCKα has been associated with cancer and validated as a drug target to treat this disease. As a consequence a large number of compounds based on Hemicholinium (HC-3) have been described. Two compounds, previously reported to inhibit the human enzyme, have recently been shown to inhibit P. falciparum CK (PfCK) and therefore their potential applications might be anticipated to other pathogens. Herein, using molecular dynamic simulations, we have firstly observed that the ATP and the choline binding site of different CK in pathogens and human are conserved, suggesting that previous compounds inhibiting the human enzyme may also interact with CKs from different pathogens. We have substantiated such observation with experimental assays showing that HsCKα1, PfCK and CpCK bind to two compounds with distinct structural features in the low µM range. Collectively, these results uncover similarities among the choline kinase binding site from different pathogenic species and the human enzyme, highlighting the feasibility of designing novel inhibitors based on the choline binding pocket.


Assuntos
Antiprotozoários/química , Colina Quinase/antagonistas & inibidores , Inibidores Enzimáticos/química , Hemicolínio 3/análogos & derivados , Proteínas de Protozoários/antagonistas & inibidores , Trifosfato de Adenosina/química , Sequência de Aminoácidos , Antiprotozoários/síntese química , Antiprotozoários/farmacologia , Domínio Catalítico , Colina/química , Colina Quinase/química , Cryptosporidium parvum/efeitos dos fármacos , Cryptosporidium parvum/enzimologia , Cryptosporidium parvum/crescimento & desenvolvimento , Inibidores Enzimáticos/síntese química , Inibidores Enzimáticos/farmacologia , Hemicolínio 3/síntese química , Hemicolínio 3/farmacologia , Humanos , Concentração Inibidora 50 , Simulação de Dinâmica Molecular , Dados de Sequência Molecular , Plasmodium falciparum/efeitos dos fármacos , Plasmodium falciparum/enzimologia , Plasmodium falciparum/crescimento & desenvolvimento , Plasmodium knowlesi/efeitos dos fármacos , Plasmodium knowlesi/enzimologia , Plasmodium knowlesi/crescimento & desenvolvimento , Estrutura Secundária de Proteína , Proteínas de Protozoários/química , Homologia de Sequência de Aminoácidos , Especificidade da Espécie
14.
Phys Rev E Stat Nonlin Soft Matter Phys ; 90(5-1): 052301, 2014 Nov.
Artigo em Inglês | MEDLINE | ID: mdl-25493790

RESUMO

A self-consistent generalized Langevin-equation theory is proposed to describe the self- and collective dynamics of a liquid of linear Brownian particles. The equations of motion for the spherical harmonics projections of the collective and self-intermediate-scattering functions, F_{lm,lm}(k,t) and F_{lm,lm}^{S}(k,t), are derived as a contraction of the description involving the stochastic equations of the corresponding tensorial one-particle density n_{lm}(k,t) and the translational (α=T) and rotational (α=R) current densities j_{lm}^{α}(k,t). Similar to the spherical case, these dynamic equations require as an external input the equilibrium structural properties of the system contained in the projections of the static structure factor, denoted by S_{lm,lm}(k). Complementing these exact equations with simple (Vineyard-like) approximate relations for the collective and the self-memory functions we propose a closed self-consistent set of equations for the dynamic properties involved. In the long-time asymptotic limit, these equations become the so-called bifurcation equations, whose solutions (the nonergodicity parameters) can be written, extending the spherical case, in terms of one translational and one orientational scalar dynamic order parameter, γ_{T} and γ_{R}, which characterize the possible dynamical arrest transitions of the system. As a concrete illustrative application of this theory we determine the dynamic arrest diagram of the dipolar hard-sphere fluid. In qualitative agreement with mode coupling theory, the present self-consistent equations also predict three different regions in the state space spanned by the macroscopic control parameters η (volume fraction) and T* (scaled temperature): a region of fully ergodic states, a region of mixed states, in which the translational degrees of freedom become arrested while the orientational degrees of freedom remain ergodic, and a region of fully nonergodic states.

17.
Ultrason Sonochem ; 21(4): 1570-7, 2014 Jul.
Artigo em Inglês | MEDLINE | ID: mdl-24530142

RESUMO

A rapid in situ biosynthesis of gold nanoparticles (AuNPs) is proposed in which a geranium (Pelargonium zonale) leaf extract was used as a non-toxic reducing and stabilizing agent in a sonocatalysis process based on high-power ultrasound. The synthesis process took only 3.5 min in aqueous solution under ambient conditions. The stability of the nanoparticles was studied by UV-Vis absorption spectroscopy with reference to the surface plasmon resonance (SPR) band. AuNPs have an average lifetime of about 8 weeks at 4 °C in the absence of light. The morphology and crystalline phase of the gold nanoparticles were characterized by transmission electron microscopy (TEM). The composition of the nanoparticles was evaluated by electron diffraction and X-ray energy dispersive spectroscopy (EDS). A total of 80% of the gold nanoparticles obtained in this way have a diameter in the range 8-20 nm, with an average size of 12±3 nm. Fourier transform infrared spectroscopy (FTIR) indicated the presence of biomolecules that could be responsible for reducing and capping the biosynthesized gold nanoparticles. A hypothesis concerning the type of organic molecules involved in this process is also given. Experimental design linked to the simplex method was used to optimize the experimental conditions for this green synthesis route. To the best of our knowledge, this is the first time that a high-power ultrasound-based sonocatalytic process and experimental design coupled to a simplex optimization process has been used in the biosynthesis of AuNPs.


Assuntos
Geranium/química , Ouro/química , Nanopartículas Metálicas/química , Extratos Vegetais/química , Folhas de Planta/química , Sonicação/métodos , Catálise , Técnicas de Química Sintética , Sonicação/instrumentação
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