Running Backwards Research Articles

“Can Time Run Backwards?”

“Can Time Run Backwards?”

Iterative Learning Control with Input Shift

Iterative learning control (ILC) is a technique to realize system inversion in a run-to-run manner. Though most of the techniques presented in the literature consider zero tracking error between the desired and achieved outputs, perfect inversion is often not feasible and in many cases not even desirable. Approximate inversion with good convergence and robustness properties (at the cost of a nonzero tracking error) has been proposed by using a forgetting factor on the input of the previous run. In this paper, approximate inversion is achieved by shifting the input of the previous run backwards in time. In addition, anticipatory ILC and current cycle feedback are used. The advantage of input shift over the use of a forgetting factor is that, when the reference trajectory is constant and the system stable, the tracking error decreases with run time. The proposed scheme is illustrated in simulation on a batch distillation system.

Perception of acceleration with short presentation times: can acceleration be used in interception?

To investigate whether visual judgments of acceleration could be used for intercepting moving targets, we determined how well subjects can detect acceleration when the presentation time is short. In a differential judgment task, two dots were presented successively. One dot accelerated and the other decelerated. Subjects had to indicate which of the two accelerated. In an absolute judgment task, subjects had to adjust the motion of a dot so that it appeared to move at a constant velocity. The results for the two tasks were similar. For most subjects, we could determine a detection threshold even when the presentation time was only 300 msec. However, an analysis of these thresholds suggests that subjects did not detect the acceleration itself but that they detected that a target had accelerated on the basis of the change in velocity between the beginning and the end of the presentation. A change of about 25% was needed to detect acceleration with reasonable confidence. Perhaps the simplest use of acceleration for interception consists of distinguishing between acceleration and deceleration of the optic projection of an approaching ball to determine whether one has to run backward or forward to catch it. We examined the results of a real ball-catching task (Oudejans, Michaels, & Bakker, 1997) and found that subjects reacted before acceleration could have been detected. We conclude that acceleration is not used in this simple manner to intercept moving targets.

The application of ground force explains the energetic cost of running backward and forward.

We compared backward with forward running to test the idea that the application of ground force to support the weight of the body determines the energetic cost of running. We hypothesized that higher metabolic rates during backward versus forward running would be directly related to greater rates of ground force application and the volume of muscle activated to apply support forces to the ground. Four trained males ran backward and forward under steady-state conditions at eight treadmill speeds from 1.75 to 3.50 m x s(-1). Rates of oxygen uptake were measured to determine metabolic rates, and inverse periods of foot-ground contact (1/tc) were measured to estimate rates of ground force application. As expected, at all eight speeds, both metabolic rates and estimated rates of ground force application were greater for backward than for forward running. At the five slowest speeds, the differences in rates of ground force application were directly proportional to the differences in metabolic rates between modes (paired t-test, P<0.05), but at the three highest speeds, small but significant differences in proportionality were present in this relationship. At one of these three higher speeds (3.0 m x s(-1)), additional measurements to estimate muscle volumes were made using a non-invasive force plate/video technique. These measurements indicated that the volume of muscle active per unit of force applied to the ground was 10+/-3% greater when running backward than forward at this speed. The product of rates of ground force application and estimated muscle volumes predicted a difference in metabolic rate that was indistinguishable from the difference we measured (34+/-6% versus 35+/-6%; means +/- s.e.m., N=4). We conclude that metabolic rates during running are determined by rates of ground force application and the volume of muscle activated to apply support forces to the ground.

Thermodynamic peptide folding path proposed

If scientists could watch a protein fold from a chain of amino acids, perhaps it would look like a film run backward: a loose, flailing strand begins to kink and coil, seemingly defying entropy as it assembles into a precise, compact structure. What sends a protein down this complex and still-mysterious path, it is believed, are fluctuating attractions in small, localized sections of the chain, which fold into short helices or sheets in preparation for global collapse into the final three-dimensional structure. For this reason, some biochemists find the behavior of short peptides particularly important. Recently, a University of California, Santa Cruz, lab led by chemistry professor Glenn L. Millhauser found some new twists in the character of such chains as they form helices. Using electron spin resonance (ESR), the scientists found that rather than forming the very common α helix, as previously thought, a group of small peptides may actually contain substantial portions of ...

Running Backwards in a Relay Race

This article contains an expert witness's report, given in a court complaint filed by a child who had been injured in a physical education activity which involved running backwards. Issues include physical education guidelines, teacher knowledge of student ability, and suitability of the surface upon which the activity occurred. (ERIC abstract IAH) Language: en

“Natural Japanese” with the “Language Repeater”

Cassettes and tapes for foreign language self-study have the rarely mentioned disadvantage that they proceed in a linear fashion: they run on until the learner presses the stop button, plays back the tape and begins again from the beginning (or from a particular counter number). Of course there are devices for repetition, for instance in language laboratories, but these are usually rather complicated to use—for instance sometimes one has to hold down a key and simultaneously find one's place by listening through the headphones to the text running backwards—and electronic repetition keys are in any case too expensive for home use. In every language, in addition to standard greetings, questions about directions and about prices etc., there are communicatively relevant sentences and phrases which the learner needs both to understand and to be able to produce if s/he is to be able to cope with the foreign environment adequately. A device providing assistance and support in learning these expressions without the time-consuming disadvantages of the linear tape programme is the “Language Repeater” manufactured by Sony. The advertising blurb claims: “Effective. Practical. Selfpaced. With Sony's Repeat Cards and the Repeater you learn Japanese the way it's really spoken—naturally.” Although there have been no controlled empirical studies of its effectiveness (probably there never will be) there can be no doubt about the practicability of this device, and its usefulness in pacing learning.

Did the Ocean Once Run Backward?

Did the Ocean Once Run Backward?

The Rise of a Middle Class and the Changing Concept of Equity in Indonesia: An Interpretation

Continuities in values and institutions in themselves reveal nothing about the direction of social change, although they may provide some indication of its speed. The significance of traditional values and institutions lies in their interaction with new elements. To understand social change it is therefore upon the new elements that one must focus. To do otherwise is like running backwards, being able to see where one has come from but not where one is going.

Dual Markov processes: Construction of a useful auxiliary process

The concept of dual, or adjoint, Markov processes was first introduced and studied by Hunt [6]. The idea seems to have been motivated by the fact that the Markov property is preserved if the direction of time is reversed: intuitively, one thinks of the dual of a Markov process as that process run backwards in time. This interpretation, while suggestive, remained for the most part unexploited for many years, while the analytic relationship between the semigroups of dual processes and the associated potential theoretic structure were explored. Duality is usually defined in terms of the resolvents (U ~) and (U s) of two processes with state space E: two resolvents are in duality relative to a a-finite measure ~ if for each c~>0 there exist functions u~(x, y) on E x E with the properties (i) us(x, ely)=u~(x, y) ~(dy), ~(dx, y)= 4(dx) u~(x, y), (ii) x~u~(x, y) is c~-excessive relative to (U~), and y ~u'(x, y) is c~-excessive relative to ([7).

Real-time reverberation generator

Since the performance of an active sonar is often limited by reverberation, an instrument which could produce accurate reverberation in real time would be valuable to sonar designers, users, and evaluators. An instrument is proposed which can satisfy their needs. It is equivalent to a digital matched-filter processor run backwards, and divides naturally into a hardware portion and a software portion. The complexity of the hardware portion depends only on the transmitter pulse length, receiver bandwidth, and the number of acoustic beams to be produced simultaneously. It employs the fast Fourier transform (FFT) algorithm, for which very fast computer processors. have been developed. The hardware portion of the reverberation generator is developed to the point where it will produce accurate reverberation if provided with the proper input information. The required input information is generated by the software portion of the instrument. It resembles the range-Doppler map produced by a matched-filter processor, except that the smearing caused by the ambiguity function of the pulse must be removed. The software portion is being developed by experimental and theoretical techniques.

Markov processes and their functional in duality

Let X and X be a pair of Markov processes in duality. Formally, this means that their transition functions are adjoint operators on L ~ of some measure space. The interpretation in terms of their paths is that X is the process X somehow run backward in time. The formal duality alone is quite powerful--after establishing some elementary results, one can prove quite amazing things just by manipulating formulae--but we want to look at the processes more from the point of view of their sample paths. In fact we backslide a bit rather quickly: the main result of w 2 is a formula which relates in a simple way quite complicated properties of the two processes, and most of the calculations in the following sections are based on it. It does make more precise in what sense X is "X run backward", however, and suggests a way to relate the functionals of one to the functionals of the other. If, for instance, A is an additive functional of one process, one can construct explicitly an additive functional A of the other which is dual to A in a quite natural sense. Because the construction is explicit, it is straightforward--given the form of the construction, "straightbackward" might be a better word--to deduce the properties of A from those of A. We consider only additive and multiplicative functionals in detail, but the method extends to other cases. The first four sections concern right continuous processes in duality and hence both A and its dual .4 must be right continuous. One could just as well consider a situation where X and A were right continuous but the dual process 2 and dual functional A were left continuous. In fact, in view of some of the complications introduced in making A right continuous, this might be not only easier, but more natural in some sense. In this spirit, the last section investigates duality without imposing continuity hypotheses. We see there that if the sample paths of one process have right limits, those of its dual must necessarily have left limits, and conversely. Let E be a locally compact separable metric space and A a point isolated from E. Let g be the topological Borel field of E u A, and b g the set of bounded g-measurable functions on E w A which vanish at A. ~2 is the space of all functions from R + to E u A which are right continuous, have left limits, and admit a lifetime ~; that is, co (t) + A if t ~ (co). As usual, we designate the coordinate variable by X~(co)=co(t), (we will often use Xt instead of X t for clarity) and let (4 ~ be the natural Borel fields of the process (Xt), with ~o = V 4 ~ Now suppose that we have two Markov processes X and X with semigroups (P~) and (4) respectively, defined canonically on ~2. This means that for each x, the semigroup (Pt) generates a measure px on (f2, ~o), and that the canonical

Effect of ouabain on the Ca 2+-dependent increase in K + permeability in depleted guinea-pig red cells

1. 1. The hypothesis that the inhibitory action of ouabain on the Ca 2+-dependent increase in K + permeability observed in depleted human red cells is mediated by changes in the intracellular level of ATP was tested by measuring simultaneously the ouabain sensitive K + loss and the concentration of ATP in depleted guinea-pig red cells in the presence and absence of external Ca 2+. 2. 2. The results showed that ouabain has opposite effects on the K + loss. Thus, in the presence of external K +, when the forward running of the Na + pump contributes to the breakdown of ATP, ouabain reduces K + loss, as observed in human red cells; in a K + free, high Na + medium when the pump running backwards induces a net synthesis of ATP (which can be detected in guinea-pig red cells but not in human red cells), ouabain increases K + loss. 3. 3. The results suggest that the action of ouabain is mediated through the changes in the intracellular level of ATP induced by the forward or reverse operation of the Na + pump.

Justice Holmes and His Hecklers

WESTBROOK Pegler, only man who ever made living out of sort of stuff that small boys scrawl on back walls and fences, has recently turned his dirty-name attack against Supreme Court Justice Oliver Wendell Holmes. Holmes, of course, has been dead these sixteen years and so Pegler, with his customary gallantry and courage, feels free to spit at Justice's memory some of choicer epithets in his vocabulary of vulgar invective. As Pegler puts it, Holmes was cynical and senile brutalitarian; he was the God of an evil cult; he was a brutal old faker; and he no more morals than pig. The owner of these lovable traits was responsible, according to limpid Peglerian logic of guilt-by-association run backwards, for subsequent sins of Alger Hiss, Lee Pressman, and scores of unnamed others who made up maze of perfidy which developed in bureaucracy soon after Roosevelt came to power-all this by direct pipe-line, through Harvard Law Review and Felix Frankfurter, straight back to arch-villain, Holmes. (Does Westbrook, I wonder, lie awake nights wishing Franklin Roosevelt had gone to Harvard Law School instead of Columbia?) Taken by itself, picture of Pegler trying to bring Holmes down (the phrase is Pegler's) is essentially comic picture. It is as though worm with delusions of grandeur were to pick on giant. For Holmes was one of finest minds and greatest spirits that American civilization has produced. And only man so bumpkin-ignorant that he thinks he need pretend ignorance in his writings could fail to recognize Holmes' stature and be little humble before it. Indeed, no one would have laughed more heartily and unmaliciously than Holmes himself at Pegler's temper tantrum in print, despite its distribution to millions of comic-book lip-readers who make up Pegler's audience and who probably confused his target-for-the-day with an outfielder, also named Holmes, formerly on Boston Braves. But Pegler's attack on Holmes unfortunately cannot be taken by itself and therefore cannot be laughed off and forgotten. Pegler, who probably never read word Holmes wrote in his life, got his lead elsewhere. He got his lead from group of men more responsible and thoughtful than he, most of whom would doubtless deplore Pegler's blast for its vulgarity and its vicious stupidity-but most of whom should recognize in what Pegler wrote reaffirmation, however offensively phrased, of their own ideas about Holmes and his philosophy of law and life.