A major contributor to this article appears to have a close connection with its subject.(June 2011) |
In biophysics and related fields, reduced dimension forms (RDFs) are unique on-off mechanisms for random walks that generate two-state trajectories (see Fig. 1 for an example of a RDF and Fig. 2 for an example of a two-state trajectory). It has been shown that RDFs solve two-state trajectories, since only one RDF can be constructed from the data, [1] where this property does not hold for on-off kinetic schemes, where many kinetic schemes can be constructed from a particular two-state trajectory (even from an ideal on-off trajectory). Two-state time trajectories are very common in measurements in chemistry, physics, and the biophysics of individual molecules [2] [3] (e.g. measurements of protein dynamics and DNA and RNA dynamics, [4] [5] [6] [7] [8] [9] [10] activity of ion channels, [11] [12] [13] enzyme activity, [14] [15] [16] [17] [18] [19] [20] [21] [22] [23] [24] quantum dots [25] [26] [27] [28] [29] [30] [31] [32] ), thus making RDFs an important tool in the analysis of data in these fields.
Since RDFs are uniquely obtained from the data, [33] [34] they have many advantages over other mathematical and statistical methods that were developed for solving two-state trajectories. [35] [36] [37] [38] [39] [40] [41] [42] [43] [44] [45] [46] [47]
A RDF is a lattice of substates, each substate represents either the on state or the off state, and has a particular number (see Figure 1). The connections are only among substates of different states. A simulation of an on-off trajectory from a RDF is made with a generalized Gillespie algorithm, where here a random jumping time is first taken from density functions that are (usually) not exponential using the rejection method, and then the specific next substate is chosen according to the jumping probabilities that are determined from the jumping time probability density functions. A RDF can have irreversible connections, yet, it generates an on-off trajectory that has the property of microscopic reversibility, meaning that the physical system fluctuates around equilibrium.
A two-state trajectory is a fluctuating signal made of on periods and off periods; an on period, and then an off period, and so on (see, Fig. 2). In most cases where this signal appears in applications in science, the trajectory is random; that is, the length of the on and off periods changes, and is a random quantity. There may be correlations in the trajectory; e.g., when we see a short off period and the next on period is relatively long (that is, long with a large probability), we say that there are off-on correlations. In principle, there are 4 independent types of correlations in two-state trajectories: on-on, on-off, off-on, and off-off. Two-state trajectories can be obtained from on-off kinetic schemes, RDFs, or any other stochastic equation of motion (with a clear on-off definition). In experiments from individual molecules, two-state trajectories are common, where from the trajectory we aim at finding the right model of the process. [48]
It was shown in Ref. 1 [1] that RDFs are unique is the sense that a particular RDF generates a particular time trajectory (in a statistical sense), and a time trajectory is associated with only one RDF. This property does not hold for on-off kinetic schemes, where from a trajectory several kinetic schemes can be constructed; see for example,. [1] RDFs are also constructed more reliably from the data than kinetic schemes. [33] Figure 3 illustrates RDFs, kinetic schemes and two-state trajectories, and the relations among these. Given a two-state trajectory (generated from any mechanism), it is safer to go from the data and construct a RDF, rather than trying to construct the kinetic scheme from the data directly. With the constructed RDF, one can find several possible kinetic schemes very accurately (usually, one eventually tries constructing a kinetic scheme from the data), where these kinetic schemes are all equivalent (with regard to the data).
PLATO is a suite of programs for electronic structure calculations. It receives its name from the choice of basis set used to expand the electronic wavefunctions.
A single-molecule experiment is an experiment that investigates the properties of individual molecules. Single-molecule studies may be contrasted with measurements on an ensemble or bulk collection of molecules, where the individual behavior of molecules cannot be distinguished, and only average characteristics can be measured. Since many measurement techniques in biology, chemistry, and physics are not sensitive enough to observe single molecules, single-molecule fluorescence techniques caused a lot of excitement, since these supplied many new details on the measured processes that were not accessible in the past. Indeed, since the 1990s, many techniques for probing individual molecules have been developed.
Harry L. Swinney is an American physicist noted for his contributions to the field of nonlinear dynamics.
Anomalous diffusion is a diffusion process with a non-linear relationship between the mean squared displacement (MSD), , and time. This behavior is in stark contrast to Brownian motion, the typical diffusion process described by Einstein and Smoluchowski, where the MSD is linear in time.
Downhill folding is a process in which a protein folds without encountering any significant macroscopic free energy barrier. It is a key prediction of the folding funnel hypothesis of the energy landscape theory of proteins.
Molecular propeller is a molecule that can propel fluids when rotated, due to its special shape that is designed in analogy to macroscopic propellers: it has several molecular-scale blades attached at a certain pitch angle around the circumference of a shaft, aligned along the rotational axis.
Single-particle tracking (SPT) is the observation of the motion of individual particles within a medium. The coordinates time series, which can be either in two dimensions (x, y) or in three dimensions (x, y, z), is referred to as a trajectory. The trajectory is typically analyzed using statistical methods to extract information about the underlying dynamics of the particle. These dynamics can reveal information about the type of transport being observed (e.g., thermal or active), the medium where the particle is moving, and interactions with other particles. In the case of random motion, trajectory analysis can be used to measure the diffusion coefficient.
Graham R. Fleming is a professor of chemistry at the University of California, Berkeley and member of the Kavli Energy NanoScience Institute based at UCB.
Hydrophobicity scales are values that define the relative hydrophobicity or hydrophilicity of amino acid residues. The more positive the value, the more hydrophobic are the amino acids located in that region of the protein. These scales are commonly used to predict the transmembrane alpha-helices of membrane proteins. When consecutively measuring amino acids of a protein, changes in value indicate attraction of specific protein regions towards the hydrophobic region inside lipid bilayer.
Fritz Peter Schäfer was a German physicist, born in Hersfeld, Hesse-Nassau. He is the co-inventor of the organic dye laser. His book, Dye Lasers, is considered a classic in the field of tunable lasers. In this book the chapter written by Schäfer gives an ample and insightful exposition on organic laser dye molecules in addition to a description on the physics of telescopic, and multiple-prism, tunable narrow-linewidth laser oscillators.
In dynamics, probability, physics, chemistry and related fields, a heterogeneous random walk in one dimension is a random walk in a one dimensional interval with jumping rules that depend on the location of the random walker in the interval.
A two-state trajectory is a dynamical signal that fluctuates between two distinct values: ON and OFF, open and closed, , etc. Mathematically, the signal has, for every either the value or .
Bioelectrodynamics is a branch of medical physics and bioelectromagnetism which deals with rapidly changing electric and magnetic fields in biological systems, i.e. high frequency endogenous electromagnetic phenomena in living cells. Unlike the events studied by the electrophysiology, the generating mechanism of bioelectrodynamic phenomenon is not connected with currents of ions and its frequency is typically much higher. Examples include vibrations of electrically polar intracellular structures and non-thermal emission of photons as a result of metabolic activity.
Amit Chakrabarti is the former William and Joan Porter Chair in Physics at Kansas State University. He currently serves as the dean of the college of arts and sciences at Kansas State University.
Jürgen Kurths is a German physicist and mathematician. He is senior advisor in the research department Complexity Sciences of the Potsdam Institute for Climate Impact Research, a Professor of Nonlinear Dynamics at the Institute of Physics at the Humboldt University, Berlin, and a 6th-century chair for Complex Systems Biology at the Institute for Complex Systems and Mathematical Biology at Kings College, Aberdeen University (UK). His research is mainly concerned with nonlinear physics and complex systems sciences and their applications to challenging problems in Earth system, physiology, systems biology and engineering.
Anatoly Boris Kolomeisky is a professor of Chemistry, Chemical and Biomolecular Engineering, Physics and Astronomy and chairman of the department of Chemistry at Rice University in Houston, Texas.
Suliana Manley is an American biophysicist. Her research focuses on the development of high-resolution optical instruments, and their application in studying the organization and dynamics of proteins. She is a professor at École Polytechnique Fédérale de Lausanne and heads the Laboratory of Experimental Biophysics.
Joshua Shaevitz is an American biophysicist and Professor of Physics at the Lewis-Sigler Institute at Princeton University in Princeton, NJ. He is known for his work in single-molecule biophysics, bacterial growth and motility, and animal behavior.
Michelle Dong Wang is a Chinese-American physicist who is the James Gilbert White Distinguished Professor of the Physical Sciences at Cornell University. She is an Investigator of the Howard Hughes Medical Institute. Her research considers biomolecular motors and single molecule optical trapping techniques. She was appointed Fellow of the American Physical Society in 2009.
Raghuveer Parthasarathy is an American biophysicist, and an Alec and Kay Keith Professor of Physics on the faculty of the University of Oregon.