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ABSTRACT: We revisit two known models of deterministically driven ratchets, which exhibit high energetic efficiency, with the goal to uncover similarities and differences in the principles of their operation. Both the models rely on adiabaticity of the potential change process, however, the adiabaticity that we deal with in the two cases is of different types, slow and fast. It is shown that in the former (latter) case the drift velocity is an even (odd) functional of the potential, with the notable consequence that for the adiabatically slow driven ratchet the necessary symmetry breaking occurs only due to time-dependent parametric perturbations, while the spatial asymmetry of the potential is a mandatory condition for the adiabatically fast driven ratchet to operate. To treat energetic characteristics, the models are restated in terms of traveling potential ratchets. With such an approach, we find that in these cases (i) the conditions of high energetic efficiency to be reached are similar, and (ii) the symmetry properties of the kinetic coefficients are different. Based on our results, a strategy for designing efficient Brownian motors is suggested.
Physical Review E 04/2012; 85(4 Pt 1):041116. · 2.26 Impact Factor
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ABSTRACT: As a model of the Brownian motor, we consider a particle moving unidirectionally under the action of two synchronously fluctuating unbiased forces, transverse and longitudinal with respect to the particle track. The former force induces track-normal transitions of the particle between the attached and detached states (with and without a periodic potential, respectively), whereas the latter drives track-parallel motion in either state. Analytical expressions of the current and efficiency are derived for different regimes, with due account of the delayed response of the system to force fluctuations. For a sawtooth potential in the attached state, we reveal several motion regimes affording the maximum current or the maximum efficiency. A special emphasis is placed on the possibility of current reversal. As shown, the interplay between two phase-shifted harmonically varied forces as well as inherent and externally induced asymmetry can lead to the emergence of multiple current reversals, thus enabling the flexible controllability of the motion direction.
Physical Review E 08/2011; 84(2 Pt 1):021104. · 2.26 Impact Factor
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ABSTRACT: We consider noise-induced reciprocating motion on the nanoscale and its rectification to directed motion using a simple model in which transitions between two fluctuating states occur through two reaction channels with fluctuating transition rates. The fluctuations of states and transition rates arise from equilibrium thermal and external nonthermal noise which is in either case position-dependent. The model is equivalent to a Brownian particle hopping in a periodic double-well potential which randomly switches between two profiles. With a nonequilibrium noise, a generalized driving force may be regarded as the sum of two forces: one resulting from energy fluctuations and the other from fluctuations of the spatial dependence of the transition rates. This suggests two mechanisms, energetic and informational, by which the motion occurs. The reciprocating motion results in directed motion if rectified by asymmetric fluctuations of potential barriers. The energy conversion efficiency is calculated and the conditions to maximize it are established.
The Journal of Physical Chemistry B 02/2010; 114(5):1959-66. · 3.70 Impact Factor
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ABSTRACT: This paper analyzes the confined motion of a Brownian particle fluctuating between two conformational states with different potential profiles and different position-dependent rate constants of the transitions, the fluctuations arising from both thermal (equilibrium) and external (nonequilibrium) noise. The model illustrates a mechanism to transduce, on the nanoscale, the energy of nonequilibrium fluctuations into mechanical energy of reciprocating motion. Expressions for the reciprocating velocity and the efficiency of energy conversion are derived. These expressions are treated in more detail in the slow-fluctuation (quasi-equilibrium) regime, by simple perturbation theory arguments, and in the fast fluctuation limit, in terms of the potential of mean force. A notable observation is that the generalized driving force of the reciprocating motion is caused by two sources: the energy contribution due to the difference between the potential profiles of the states and the entropic contribution due to the difference between the position-dependent rate constants. Two illustrative examples are presented, where one of the two sources can be ignored and an exact solution is allowed. Among other aspects, we also discuss the ways to construct a molecular motor based on the reciprocating engine.
The Journal of Physical Chemistry A 10/2007; 111(38):9486-93. · 2.95 Impact Factor
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ABSTRACT: The severe acute respiratory syndrome (SARS) outbreak in 2003 affected 29 countries. The SARS outbreak was unique in its rapid transmission and it resulted in heavy stress in first-line healthcare workers, particularly in the emergency department.
: To determine the influence of SARS on the psychological status, including post-traumatic stress disorder (PTSD) symptoms, of the staff in the emergency department.
To investigate whether different working conditions in the hospital led to different psychological effects on healthcare workers, the psychological effect on emergency department staff in the high-risk ward was compared with that on psychiatric ward staff in the medium-risk ward. Davidson Trauma Scale-Chinese version (DTS-C) and Chinese Health Questionnaire-12 (CHQ-12) items were designed to check the psychological status of the staff in the month after the end of the SARS outbreak.
86 of 92 (93.5%) medical staff considered the SARS outbreak to be a traumatic experience. The DTS-C scores of staff in the emergency department and in the psychiatric ward were significantly different (p = 0.04). No significant difference in CHQ score was observed between the two groups. Emergency department staff had more severe PTSD symptoms than staff in the psychiatric ward.
SARS was a traumatic experience for healthcare providers in Taiwan. Most staff in the emergency department and in the psychiatric ward had PTSD. Emergency department staff had more severe PTSD symptoms than staff in the psychiatric ward.
Emergency Medicine Journal 02/2007; 24(1):12-7. · 1.44 Impact Factor
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ABSTRACT: For a flashing ratchet with periodic potentials fluctuating via random shifts of one-half period, a high efficiency is shown to result from two mechanisms. The previously reported one [Yu. A. Makhnovskii, Phys. Rev. E 69, 021102 (2004); V. M. Rozenbaum, JETP Lett. 79, 388 (2004)] is realized in the near-equilibrium region and implies, first, the presence of a high barrier V0 blocking the reverse movement of a Brownian particle and, second, identical, though energy-shifted, portions of the asymmetric flat potential profile on both half periods. We report another mechanism acting far from equilibrium, typical of strongly asymmetric potentials which are shaped identically on both half periods with a large energetic shift DeltaV . The two mechanisms exhibit radically different limiting behavior of the maximum possible efficiency: eta(m) approximately 1-exp (-beta V0 /2) for the former and eta(m) approximately 1-ln (2betaDeltaV) /betaDeltaV for the latter ( beta being the reciprocal temperature in energy units). The flux and the efficiency for a Brownian motor with a piecewise-linear potential are calculated using the transfer matrix method; an exact analytical solution can thus be obtained for an extremely asymmetric sawtooth potential, the simplest example of the second high-efficiency mechanism. As demonstrated, the mechanisms considered are also characteristic of a two-well periodic potential treated in terms of the kinetic approach.
Physical Review E 05/2005; 71(4 Pt 1):041102. · 2.26 Impact Factor
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ABSTRACT: A system is considered in which transitions between two states occur through two reaction channels. Because of coupling with an external process which consists of cyclic switching between two regimes (each characterized by a certain fixed set of rate constants), the net circulation flux arises in the system even in the absence of an external generalized force. Such a mechanism underlying a catalytic wheel of many biological processes is considered as a Brownian motor. The basic operational motor characteristics are calculated for the regular and random inter-regime switching, being better in the former case and reaching the optimum at equal relaxation-to-lifetime ratios for the two regimes. The general Brownian motor formalism is exemplified by two particular realizations, the electroconformational-coupling model and the flashing-potential model. The former concerns enzymatically catalyzed ligand pumping through a membrane, and the latter describes particle motion under two sets of potential wells and barriers. Because of a unified thread between the two models, their parameters are interrelated, and all of the relevant conclusions are valid for either of them. In the tight coupling limit, the optimal conditions are analyzed, and they imply that a catalytic wheel operated by the Brownian motor works with the maximum output energy (useful work) or with the maximum efficiency tending to unity under certain conditions.
09/2004;
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ABSTRACT: As a simple model of the Brownian motor, we consider hopping motion of a particle in a periodic asymmetric double-well potential which randomly switches between two states. The potential profiles of the states are identical but shifted by half a period. The current and the efficiency are explicitly calculated as functions of the parameters of the model, including also a load force. Such a flashing ratchet is shown to be particularly efficient, with the efficiency tending to unity when the highest peak of the potential is high enough to suppress the backward motion.
Physical Review E 03/2004; 69(2 Pt 1):021102. · 2.26 Impact Factor
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ABSTRACT: Snakebite may be complicated with bacteria infections, most of which are Gram-negative bacillus. Snakebite complicated with Vibrio vulnificus infection has not been reported previously. Vibrio vulnificus infection is characterized by a necrotizing wound infection similar to the local lesion of severe snakebite. In Vibrio infections, aggressive debridement with the administration of strong antibiotics as early as possible is the only effective treatment. We report a 79-y-o man who suffered from snakebite on the right palm with rapid progression of hemorrhagic bulla, necrotizing fasciitis, compartment syndrome, and septic shock. Vibrio vulnificuswas cultured from necrotic tissue after aggressive debridement and fasciotomy. The patient recovered from antibiotic treatment and several courses of reconstruction surgery. Severe bacteria infection, such as caused by Vibrio vulnificus, should be considered in snakebite cases refractory to antivenin dosage.
Veterinary and human toxicology 11/2001; 43(5):283-5.
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ABSTRACT: Clinical presentation of aortic dissection is similar to that of acute myocardial infarction (AMI). Clinical differential diagnoses from lethal chest pain in emergency department include AMI, aortic dissection, pulmonary embolism, tension pneumothorax, etc. Thrombolytic therapy for recanalization of thrombotic occluded coronary artery in AMI must be considered, but it is absolutely contraindicated for aortic dissection. However, AMI secondary to aortic dissection is a rare condition, which might be caused by compression of the coronary arteries by a hematoma or extension of the dissection into the coronary arterial wall. Surgery is the first choice for AMI secondary to aortic dissection caused by extension of dissection into the coronary arterial wall. We present a case of inferior wall AMI caused by type I aortic dissection with presentation of chest pain and hemiparaplegia of right lower limb.
Zhonghua yi xue za zhi = Chinese medical journal; Free China ed 10/2001; 64(9):535-9.
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ABSTRACT: The coincidence of hemolysis, elevated liver enzymes, and low platelet count (HELLP) syndrome and cortical blindness is an uncommon but very dramatic event. We describe a case of HELLP syndrome complicating with acute cortical blindness before delivery. A 27 year-old woman, gravida 1, para 0, with normal medical history, was referred to our emergency department at the 33th week of gestation due to headache, vomiting, and blurred vision. The ophthalmologic examination showed intact pupillary light reflexes and normal ophthalmoscopic findings, but no light perception in either eye. Brain computed tomography showed normal findings. HELLP syndrome and preeclampsia was diagnosed based on the findings of hypertension and proteinuria as well as laboratory data. Prompt delivery was performed in order to achieve good maternal and neonatal outcomes.
Zhonghua yi xue za zhi = Chinese medical journal; Free China ed 09/2001; 64(8):482-5.
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ABSTRACT: Nitrofen has been banned in Taiwan since January 1, 1983 due to its tetrogenicity. A 78-y-o female consumed about 500 ml of herbicide, labeled as nitrofen, in a suicide attempt. Consciousness disturbance occurred immediately. After 9 h, bloody-tarry stool was noted. Hematemesis occurred 19 h later. Hepatotoxicity and nephrotoxicity also developed. Twitching of head and both upper extremities lasting 20-30 sec and up to 5 min developed on day 3. Sometimes an upward gaze with the face turned to the right or a convulsion of the right upper extremity was observed. EEG showed alpha coma, generalized slow spike-and-wave complexes, and isolated generalized sharp waves mainly in the left occipital area. On day 7, endotracheal intubation was performed due to apnea; she expired on day 9. The pesticide was found to contain butachlor and chlornitrofen. The Agricultural Committee prohibited the marketing of chlornitrofen due to its generation of tumors in animals. The combination of butachlor and chlornitrofen can result in consciousness disturbance, leucocytosis, gastrointestinal hemorrhage, rhabdomyolysis, hypocalcemia, hypoalbuminemia, elevated amylase, nephrotoxicity, hepatotoxicity, seizures and death. The cytotoxicity of butachlor may be related to the patient's death. Active components of pesticides should be checked if the clinical course of a poisoned patient is unusual to allow appropriate interventions.
Veterinary and human toxicology 09/2001; 43(4):212-4.
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Gastrointestinal Endoscopy 08/2001; 54(1):116-7. · 4.88 Impact Factor
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ABSTRACT: We present the dynamic scaling behavior for the specific viscosity and diffusion coefficient of a single membrane and membranes with nonzero concentration in solution. Starting from the membrane free energies, we derive their Langevin equations. The corresponding Kirkwood diffusion equation, describing the time evolution in configuration space, contains two kinds of time scales that are separated by the external dimension 4/(2-D) where D is the dimension of the internal space. These time scale separation behaviors depend strongly on the hydrodynamic screening effect. For a single membrane solution, we resolve the dynamic scaling exponents for the diffusion coefficient and intrinsic viscosity by the dimension reduction method. For a concentrated membrane solution, the effective excluded volume strength and draining parameter are introduced. The effective medium argument is applied to obtain a concentration dependent power law form for the specific viscosity and diffusion coefficient, whose results contribute to a fundamental understanding of membrane in solution and of hydrodynamic screening and excluded volume effects in many different solvents.
Physical Review E 07/2001; 63(6 Pt 1):061207. · 2.26 Impact Factor
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ABSTRACT: Therapeutic endoscopy with isotonic saline-epinephrine (ISE) injection is a convenient and widely used procedure for hemostasis in upper gastrointestinal bleeding. We retrospectively evaluated 36 patients (from January 1996 to April 1999) who had been diagnosed with recent or active bleeding due to Mallory-Weiss tears in emergency endoscopic examination. The endoscopic hemostatic method with ISE injection was performed in 15 of 36 patients. The other 21 patients received conservative treatment with hemodynamic support. Patient's clinical data, laboratory data, transfusion requirements, endoscopic findings, and length of hospital stays were evaluated. Initial hemoglobin was significantly lower in the ISE group than the conservative treatment group (9.74 +/- 2.86 g/dL vs. 12.57 +/- 2.80 g/dL, respectively; p < 0.01). Mean transfusion requirements were significantly higher in the ISE group than the conservative treatment group (7.26 +/- 8.78 units vs. 2.85 +/- 6.21 units, respectively; p < 0.1). Patients in the ISE group were supposed to be having a more severe bleeding episode. Most patients achieved initial hemostasis in the ISE group and the conservative treatment group (93% and 95%, respectively). The rebleeding rate was also similar in both groups (1 in 15 in the ISE group and I in 21 in the conservative treatment group). There was no significant difference in length of hospital stay and rebleeding between these two groups (3.47 +/- 1.92 days vs. 2.47 +/- 1.47 days, respectively: p = 0.89). The endoscopic ISE injection is an inexpensive, simple, convenient therapeutic method and it can achieve initial hemostasis for active Mallory-Weiss tears.
Journal of Clinical Gastroenterology 02/2001; 32(2):119-22. · 3.16 Impact Factor
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Journal of toxicology. Clinical toxicology 02/2001; 39(4):423-4.
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ABSTRACT: Fifty patients with glyphosate-surfactant oral ingestion were studied with upper gastrointestinal (UGI) endoscopic grading using Zargar's modified grading system for mucosal corrosive injury. Esophageal injury was seen in 68% of the patients, gastric injury in 72%, and duodenal injury in 16%. There were no grade 3 injuries. The upper gastrointestinal tract injuries caused by glyphosate-surfactant were minor in comparison with those by other strong acids. The WBC count, amount of glyphosate-surfactant ingested, length of hospital stay and the occurrence of serious complications increased markedly in the group which had grade 2 esophageal injuries. Thus, the severity of the esophageal injuries may be a prognostic factor for the patient with glyphosate-surfactant ingestion. The UGI endoscopy may be indicated for grading esophageal injury in patients who have ingested glyphosate-surfactant in amounts greater than 100 ml. Physicians should pay more attention to the patients with grade 2 or 3 esophageal injuries to prevent serious complications and to provide aggressive supportive care.
Human & Experimental Toxicology 09/1999; 18(8):475-8. · 1.77 Impact Factor
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ABSTRACT: A 27-year-old robust man, without any medical and surgical history, attempted to commit suicide by consumption of 300 cc (44.1%, 132.3 g) basagran, a readily available herbicide. This poisoning resulted in vomiting, fever, sweating, pipe-like muscle rigidity, sinus tachycardia, drowsiness, leukocytosis, rhabdomyolysis and hepatorenal damage. Emperical treatment with bromocriptine was temporally associated with resolution of above signs and symptoms. His clinical presentations and the effect of bromocriptine may be indicative that basagran poisoning mimicks neuroleptic malignant syndrome.
Human & Experimental Toxicology 09/1999; 18(8):493-4. · 1.77 Impact Factor
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ABSTRACT: 1. In animal studies, TPTA was found to be neurotoxic. In humans, variable CNS pictures have been described with or without significant EEG findings. Brain CT does not usually reveal any abnormalities. 2. Our patient presented with intermittent unique spontaneous involuntary movement of hands, facial twitching, silly smile and crying. Diplopia, drowsiness, giddiness, vertigo, bidirectional nystagmus, impairment of calculation ability, as well as disorientation to time, people and place also developed. EEG showed mild cortical dysfunction without seizures. MRI and Tc-99m HMPAO brain SPECT revealed no significant findings. TPTA may cause cellular dysfunction of brain without structural damage, which results in variable CNS clinical presentations. 3. Nadir of leucopenia was noted on the sixth day after consumption of TPTA. Liver impairment occurred on the ninth day. Borderline demyelinated neuropathy developed on the fifty-third day. CNS abnormalities, delayed peripheral neuropathy, hepatitis and leucopenia deserve monitoring for a prolonged period, even when the victim initially presents with GI upset only after consumption of TPTA.
Human & Experimental Toxicology 08/1998; 17(7):403-5. · 1.77 Impact Factor
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ABSTRACT: Administration of phenylpropanolamine (PPA) is a rare cause of intracerebral hemorrhage. We present the case of a young female patient with arteriovenous malformation who suffered an intracerebral hemorrhage after ingestion of diet pills containing PPA. The literature on PPA-related intracerebral hemorrhage is also reviewed. This is the first report of PPA-associated intracerebral hemorrhage in a patient with pathology-proven arteriovenous malformation of the brain. Because intracerebral hemorrhage may develop as a side effect of PPA when patients take the manufacturer's recommended dose, especially in patients with vascular abnormalities, we conclude that this medicine should be prescribed carefully and patients should be closely monitored by experienced physicians. Furthermore, its use should be contraindicated in patients who have, or possibly have, a family history of vascular abnormalities.
Zhonghua yi xue za zhi = Chinese medical journal; Free China ed 08/1998; 61(7):432-5.
