Escape of a Uniform Random Walk from an Interval

We study the first-passage properties of a random walk in the unit interval in which the length of a single step is uniformly distributed over the finite range [-a,a]. For a of the order of one, the exit probabilities to each edge of the interval and the exit time from the interval exhibit anomalous properties stemming from the change in the minimum number of steps to escape the interval as a function of the starting point. As a decreases, first-passage properties approach those of continuum diffusion, but non-diffusive effects remain because of residual discreteness effectsComment: 8 pages, 8 figures, 2 column revtex4 forma

Distribution of dwell times of a ribosome: effects of infidelity, kinetic proofreading and ribosome crowding

Ribosome is a molecular machine that polymerizes a protein where the sequence of the amino acid residues, the monomers of the protein, is dictated by the sequence of codons (triplets of nucleotides) on a messenger RNA (mRNA) that serves as the template. The ribosome is a molecular motor that utilizes the template mRNA strand also as the track. Thus, in each step the ribosome moves forward by one codon and, simultaneously, elongates the protein by one amino acid. We present a theoretical model that captures most of the main steps in the mechano-chemical cycle of a ribosome. The stochastic movement of the ribosome consists of an alternating sequence of pause and translocation; the sum of the durations of a pause and the following translocation is the time of dwell of the ribosome at the corresponding codon. We derive the analytical expression for the distribution of the dwell times of a ribosome in our model. Whereever experimental data are available, our theoretical predictions are consistent with those results. We suggest appropriate experiments to test the new predictions of our model, particularly, the effects of the quality control mechanism of the ribosome and that of their crowding on the mRNA track.Comment: This is an author-created, un-copyedited version of an article accepted for publication in Physical Biology. IOP Publishing Ltd is not responsible for any errors or omissions in this version of the manuscript or any version derived from it. The definitive publisher authenticated version is available online at DOI:10.1088/1478-3975/8/2/02600

The vegetation of the Meggyes Marsh in the starting phase of rehabilitation

In the middle of the last century enormous water regulation works were implemented in the flood plain of the River Tisza in order to open large areas for intensive agricultural production. In the recent past (1970s) agricultural amelioration has been the most significant of human-induced factors threatening the wetlands. Fortunately, the dominant wetland types have survived these unfavourable conditions. The remains of them are still of inestimable value for nature conservation, because alkaline marshes and shallow ponds have almost completely disappeared from other parts of Europe. Consequently, it is the basic duty of nature conservation to preserve or restore the residual natural or semi-natural wetlands, as well as to revive the one-time connections among units that have become separated from each other. Accordingly, Hortobagy National Park aims at restoring and maintaining the original water regime of the water-related habitats in order to arrive at the most natural conditions possible. Hydrobiological research on a rehabilitated marsh was started in 1996, the year of the first flooding, while in 1997 the investigations were completed with a vegetation survey. In the present paper, information is provided on the hydrobiological conditions observed in the area, and the principal botanical transformations of the flooded marsh are summarized. In the starting phase of the rehabilitation significant changes took place as the degraded homogenous vegetation became altered by - when considering species composition and structure - a more diverse type of vegetation. Both botanical and hydrobiological data indicated an alkaline marsh character

The vegetation of the Meggyes Marsh in the starting phase of rehabilitation

In the middle of the last century enormous water regulation works were implemented in the flood plain of the River Tisza in order to open large areas for intensive agricultural production. In the recent past (1970s) agricultural amelioration has been the most significant of human-induced factors threatening the wetlands. Fortunately, the dominant wetland types have survived these unfavourable conditions. The remains of them are still of inestimable value for nature conservation, because alkaline marshes and shallow ponds have almost completely disappeared from other parts of Europe. Consequently, it is the basic duty of nature conservation to preserve or restore the residual natural or semi-natural wetlands, as well as to revive the one-time connections among units that have become separated from each other. Accordingly, Hortobagy National Park aims at restoring and maintaining the original water regime of the water-related habitats in order to arrive at the most natural conditions possible. Hydrobiological research on a rehabilitated marsh was started in 1996, the year of the first flooding, while in 1997 the investigations were completed with a vegetation survey. In the present paper, information is provided on the hydrobiological conditions observed in the area, and the principal botanical transformations of the flooded marsh are summarized. In the starting phase of the rehabilitation significant changes took place as the degraded homogenous vegetation became altered by - when considering species composition and structure - a more diverse type of vegetation. Both botanical and hydrobiological data indicated an alkaline marsh character

Csirkeér mechanikai vizsgálata egyedi építésű kísérleti berendezéssel

A szív- és érrendszeri betegségek évtizedek óta tizedelik az emberiséget. Az erek in vivo vizsgálata nagy segítséget nyújt numerikus modellek és szimulációk fejlesztéséhez, amelyek segítségével az orvosok érdemben tudnak javítani az életminőségen. Az ilyen modellekhez az erek különböző mechanikai jellemzői a bemeneti adatok. Az erek több ilyen mechanikai tulajdonságának, például a rugalmassági modulusznak és szakítószilárdságnak, meghatározása szakítóvizsgálattal történik. Kutatásunk során egy erek kéttengelyű szakítására is alkalmas kísérleti berendezést fejlesztettünk és teszteltünk, amelyet csirkeerek vizsgálatán keresztül mutatunk be

Competition for finite resources

The resources in a cell are finite, which implies that the various components of the cell must compete for resources. One such resource is the ribosomes used during translation to create proteins. Motivated by this example, we explore this competition by connecting two totally asymmetric simple exclusion processes (TASEPs) to a finite pool of particles. Expanding on our previous work, we focus on the effects on the density and current of having different entry and exit rates.Comment: 15 pages, 9 figures, v2: minor revisions, v3: additional reference & minor correction

The Blazhko behaviour of RR Geminorum I - CCD photometric results in 2004

Extended CCD monitoring of RR Gem revealed that it is a Blazhko type RRab star with the shortest Blazhko period (7.23d) and smallest modulation amplitude (Delta Mmax<0.1 mag) currently known. The short period of the modulation cycle enabled us to obtain complete phase coverage of the pulsation at each phase of the modulation. This is the first multicolour observation of a Blazhko star which is extended enough to define accurate mean magnitudes and colours of the variable at different Blazhko phases. Small, but real, changes in the intensity mean colours at different Blazhko phases have been detected. The Fourier analysis of the light curves shows that, in spite of the mmag and smaller order of the amplitudes, the triplet structure is noticeable up to about the 14th harmonic. The modulation is concentrated to a very narrow, 0.2 phase range of the pulsation, centred on the supposed onset of the H emission during rising light. These observational results raise further complications for theoretical explanation of the long known but poorly understood Blazhko phenomenon.Comment: 10 pages, 12 figures, 3 tables. Accepted for publication in Astronomy and Astrophysic

An International Ultraviolet Explorer Archival Study of Dwarf Novae in Outburst

We present a synthetic spectral analysis of nearly the entire far ultraviolet International Ultraviolet Explorer (IUE) archive of spectra of dwarf novae in or near outburst. The study includes 46 systems of all dwarf nova subtypes both above and below the period gap. The spectra were uniformly analyzed using synthetic spectral codes for optically thick accretion disks and stellar photospheres along with the best-available distance measurements or estimates. We present newly estimated accretion rates and discuss the implications of our study for disk accretion physics and CV evolution.Comment: Accepted for publication in the ApJ, Part