scholarly journals Biophysical comparison of ATP synthesis mechanisms shows a kinetic advantage for the rotary process

2016 ◽  
Vol 113 (40) ◽  
pp. 11220-11225 ◽  
Author(s):  
Ramu Anandakrishnan ◽  
Zining Zhang ◽  
Rory Donovan-Maiye ◽  
Daniel M. Zuckerman

The ATP synthase (F-ATPase) is a highly complex rotary machine that synthesizes ATP, powered by a proton electrochemical gradient. Why did evolution select such an elaborate mechanism over arguably simpler alternating-access processes that can be reversed to perform ATP synthesis? We studied a systematic enumeration of alternative mechanisms, using numerical and theoretical means. When the alternative models are optimized subject to fundamental thermodynamic constraints, they fail to match the kinetic ability of the rotary mechanism over a wide range of conditions, particularly under low-energy conditions. We used a physically interpretable, closed-form solution for the steady-state rate for an arbitrary chemical cycle, which clarifies kinetic effects of complex free-energy landscapes. Our analysis also yields insights into the debated “kinetic equivalence” of ATP synthesis driven by transmembrane pH and potential difference. Overall, our study suggests that the complexity of the F-ATPase may have resulted from positive selection for its kinetic advantage.

Author(s):  
Christopher Wordingham ◽  
Pierre-Yves Taunay ◽  
Edgar Choueiri

Abstract A first-principles approach to obtain the attachment length within a hollow cathode with a constrictive orifice, and its scaling with internal cathode pressure, is developed. This parameter, defined herein as the plasma density decay length scale upstream of (away from) the cathode orifice, is critical because it controls the utilization of the hollow cathode insert and influences cathode life. A two-dimensional framework is developed from the ambipolar diffusion equation for the insert-region plasma. A closed-form solution for the plasma density is obtained using standard partial differential equation techniques by applying an approximate boundary condition at the cathode orifice plane. This approach also yields the attachment length and electron temperature without reliance on measured plasma property data or complex computational models. The predicted plasma density profile is validated against measurements from the NSTAR discharge cathode, and calculated electron temperatures and attachment lengths agree with published values. Nondimensionalization of the governing equations reveals that the solution depends almost exclusively on the neutral pressure-diameter product in the insert plasma region. Evaluation of analytical results over a wide range of input parameters yields scaling relations for the variation of the attachment length and electron temperature with the pressure-diameter product. For the range of orifice-to-insert diameter ratio studied, the influence of orifice size is shown to be small except through its effect on insert pressure, and the attachment length is shown to be proportional to the insert inner radius, suggesting high-pressure cathodes should be constructed with larger-diameter inserts.


2011 ◽  
Vol 2011 ◽  
pp. 1-21 ◽  
Author(s):  
Field Cady ◽  
Yi Zhuang ◽  
Mor Harchol-Balter

We provide a stochastic analysis of hard disk performance, including a closed form solution for the average access time of a memory request. The model we use covers a wide range of types and applications of disks, and in particular it captures modern innovations like zone bit recording. The derivation is based on an analytical technique we call “shuffling”, which greatly simplifies the analysis relative to previous work and provides a simple, easy-to-use formula for the average access time. Our analysis can predict performance of single disks for a wide range of disk types and workloads. Furthermore, it can predict the performance benefits of several optimizations, including short stroking and mirroring, which are common in disk arrays.


Author(s):  
Valdas Chaika

Abstract Torsional vibration of two flexibly coupled reciprocating machines is investigated. The rotors of the machines are connected by elastic couplings of several types. The system is excited by a harmonic torque. The excitation frequency is proportional to the rotational speed which varies within a wide range. The motion of the system is described by nonlinear ordinary differential equations. These are linearized for the specific case of the rotor assembly design. Applying impedance functions, a closed-form solution of the equations of motion is derived. Three different cases of the system response are analyzed in the frequency domain. The passive vibration control of the rotor assembly using the centrifugal coupling is investigated. An analytical synthesis technique of the coupling parameters is devised.


Author(s):  
Han-Bum Surh ◽  
Jong Wook Kim ◽  
Min Kyu Kim ◽  
Min-Gu Won ◽  
Moon Ki Kim ◽  
...  

The stress intensity factor (SIF) is the major fracture mechanics parameter in LEFM concept. Since the SIF can be used for not only calculation of J-integral based on the GE/EPRI and reference stress method but also evaluation of fatigue crack growth, an accurate estimation of the SIF is an important issue for the piping in nuclear power plant. Recently, there is a need to develop the SIF solution which can cover wide geometric variables since there are on-going efforts that are developing next generation reactors in Korea, which is designed to thin-walled structures. For the through-wall cracked straight pipes, many researchers have proposed the SIF solutions which can cover wide range of wall thickness. However, since only limited solutions have been proposed yet for the through-wall cracked elbows, a research related to the SIF estimation for the elbows with wide geometric variables should be performed. In this study, the extended SIF solution for circumferential through-wall cracked elbows subjected to in-plane bending is proposed as the tabulated form through the finite element (FE) analyses. Wide elbow geometries are selected to range between 5 and 50 of Rm/t and range between 2∼20 of Rb/Rm. The existing solutions are then reviewed by comparing with the FE results. Furthermore, effects of geometric variables on the SIF are addressed through systematic investigation of FE based SIF results. These investigated results are expected to contribute to the development of closed form solution for the circumferential through-wall cracked elbows subjected to in-plane bending.


2006 ◽  
Vol 03 (03) ◽  
pp. 263-277 ◽  
Author(s):  
HOSSEIN ROUHANI ◽  
MANSOUR NIKKHAH BAHRAMI ◽  
BABAK NADJAR ARAABI ◽  
CARO LUCAS

A thorough analysis of cylindrical shells' dynamical behavior is essential in many different industrial design problems, and particularly in electric motor design. Shell vibration equations form a set of partial differential equations of order eight, where their closed form solution is only known for few special cases with a few known boundary conditions along with many not necessarily realistic assumptions. On the other hand, finite element based numerical solutions does not yield a lumped model that can be regarded as a general solution for natural frequencies of cylindrical shells. In this paper, a neurofuzzy model for natural frequencies of cylindrical shells is developed. At first, natural frequencies are calculated for a wide range of cylindrical shells' dimensions, using either closed form solution or finite element method. Gathered data is exploited for training of a Locally Linear Neurofuzzy Network, which yields a general model for calculation of natural frequencies of cylindrical shells. While the developed neurofuzzy model may be used in different design problems that deals with cylindrical shells, as a case study, the proposed model along with an evolutionary algorithm are utilized in the optimal design of a Switched Reluctance motor.


2014 ◽  
Vol 58 (04) ◽  
pp. 185-200 ◽  
Author(s):  
M. G. Morabito

Recently there has been increasing interest in the fluid-structure interaction problem of planning hull bottom structure during slamming events. Significant work has been done in estimating the bottom pressures that occur during a slam and incorporating this into structural models of planing craft. In this article, empirical equations for the pressure distribution on prismatic planing hulls are developed, including both hydrostatic and hydrodynamic effects, deadrise variation, trim, and wetted length. The empirical method is based on relevant experimental measurements of planing hull bottom pressures that have been made over an 80-year period. This analysis may readily be extended to the impact problem by substitution of an equivalent planing velocity, which is discussed in the article. The end result is a closed form solution for bottom pressures on prismatic planing craft that can be rapidly calculated using a simple spreadsheet. The method is applicable for deadrise angles from 0 to 40, trim angles up to 30, and wetted lengths up to five beams. This wide range of parameters is significantly larger than most current models. The empirical method is modular, allowing for substitution of more accurate formulae as more data become available in the future.


2019 ◽  
Vol 56 (1) ◽  
pp. 135-143 ◽  
Author(s):  
Cheng Lin ◽  
Randall Wu

Determination of vertical effective stress along piles is an essential part of calculation of both pile axial and lateral capacities under scour conditions. However, the current design manuals including those from the US Federal Highway Administration (FHWA) and American Petroleum Institute (API) recommend different methods for calculating vertical effective stress. Moreover, they are effective only for restricted scour-hole dimensions. This study presents an improved closed-form solution that allows estimation of the vertical effective stress for a wide range of scour-hole dimensions including scour depth, width, and slope angle. Using the improved analytical solution for stress, API p–y curves for sand were modified to compute pile lateral capacity at different scour-hole conditions. Based on a series of parametric analyses for laterally loaded piles in sand, errors of calculation using the existing methods were quantified and a simplified method was proposed for practical applications. Effects of different scour-hole dimensions on both vertical effective stress and pile lateral capacity were also discussed.


1978 ◽  
Vol 100 (1) ◽  
pp. 88-94 ◽  
Author(s):  
M. Hashish ◽  
M. P. duPlessis

The study attempts to develop a theory for the penetration of a wide range of solid materials by continuous high-velocity water jets. The theory is based on a control volume analysis to determine the hydrodynamic forces acting on the solid boundaries of the cutting slot. A Bingham model is used to describe the time-dependent stress-strain relationship of the solid material. The coupled fluid-solid mechanics equations are simplified to yield a closed-form solution in the form of a nondimensional cutting equation zdn=1−σcρV122Cf√π[1−e−(2Cf/√π)·(ρV1/η)·(V1/u)] which satisfies all the limiting conditions of practical cutting applications. Published experimental results from cutting tests with a wide range of fibrous, granular and crystalline material are used to obtain mean values of the friction (Cf) and damping coefficients (η) which are used with the compressive yield strength (σc) to characterize different materials. The theory presents a basis for developing more exact cutting equations by choosing the optimum rheological model for a particular material.


2021 ◽  
pp. 108128652110545
Author(s):  
S Kiana Naghibzadeh ◽  
Noel Walkington ◽  
Kaushik Dayal

Accretion and ablation, i.e., the addition and removal of mass at the surface, are important in a wide range of physical processes, including solidification, growth of biological tissues, environmental processes, and additive manufacturing. The description of accretion requires the addition of new continuum particles to the body, and is therefore challenging for standard continuum formulations for solids that require a reference configuration. Recent work has proposed an Eulerian approach to this problem, enabling side-stepping of the issue of constructing the reference configuration. However, this raises the complementary challenge of determining the stress response of the solid, which typically requires the deformation gradient that is not immediately available in the Eulerian formulation. To resolve this, the approach introduced the elastic deformation as an additional kinematic descriptor of the added material, and its evolution has been shown to be governed by a transport equation. In this work, the method of characteristics is applied to solve concrete simplified problems motivated by biomechanics and manufacturing. Specifically, (1) for a problem with both ablation and accretion in a fixed domain and (2) for a problem with a time-varying domain, the closed-form solution is obtained in the Eulerian framework using the method of characteristics without explicit construction of the reference configuration.


1998 ◽  
Vol 65 (4) ◽  
pp. 851-857 ◽  
Author(s):  
M. J. Leamy ◽  
J. R. Barber ◽  
N. C. Perkins

This study is motivated by the need to understand the elastodynamic response of belts in frictional contact with pulleys. To this end, a simplified model for belt/pulley contact is used to investigate the dynamic response of a belt subject to a train of harmonic tension waves. Through a nondimensionalization, a single dimensionless parameter Ω is identified which governs the dynamic response. A numerical solution is developed and exercised over a wide range of values of Ω An approximate closed-form solution is derived assuming the belt stretches quasi-statically, and is shown to yield accurate results for small values of Ω Reported results include the distortion of an initially harmonic tension wave, the energy reflected from the frictional support, and the distance harmonic waves penetrate into the support. The results suggest that the quasi-static stretching assumption may be further utilized as a modeling simplification for belt drives characterized by values of Ω <1/3.


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