Homogeneous Fragments Research Articles

Room Temperature Consolidation of Al and B<sub>4</sub>C Composite Powder by Equal Channel Angular Pressing

The aim at the present work is to study the consolidation behavior of Al and B4Ccomposite powder processed by Equal Channel Angular Pressing (ECAP) at room temperature. The composition of the composite powder is 95 wt% Al and 5 wt% B4C. The Al-B4C composite powder is subjected to ECAP through processing route A up to 4 passes. The ECAP die used for densification has 90° channel angle and 20° corner angle. It is found that the density and hardness of the composite are improved as the ECAP passes is increased. The microstructure is homogeneous and partial fragmentation of reinforcement is observed. Density and hardness measured after four ECAP are 97% and 98 HV. The improvement of density and hardness is the due strain enhances consolidation of powders during ECAP.

Impact fragmentation of nanoscale projectiles at ultrahigh striking velocities

Molecular-dynamics simulations of the classic Taylor experiment are performed to investigate some general trends of impact fragmentation at ultra-high striking velocities. The striking velocities of flat-ended, monocrystalline, nanoscale pillars (nanoprojectiles) range from 0.34 km/s (Mach 1) to 30 km/s to explore qualitative effects on the fragment mass distribution. These atomistic simulations offer insight into evolution of the fragment distribution and its dependence upon the striking velocity. According to the simulation results, distribution of the fragment masses following hypervelocity impacts of energy sufficient to ensure that the fragmentation problem is statistically well posed, is well represented by the bilinear (bimodal) exponential distribution commonly observed during high-energy homogeneous fragmentation events. At more moderate striking velocities, a mixing of fragments from different fragmentation intensity events—that is, the more pronounced statistical heterogeneity—results in the distribution of fragment masses that appears to follow the trilinear (trimodal) exponential distribution due to the occurrence of a large-fragment tail in addition to the bilinear exponential part. The maximum fragment mass is studied from the standpoint of the striking velocity as well as a set of state parameters: the instantaneous kinetic temperature and the selected stress and strain invariants; corresponding phenomenological relationships are suggested for the investigated hypervelocity impact range.

Survival of homogeneous fragmentation processes with killing

Nous considérons un processus de fragmentation homogène tué à une barrière exponentielle. À l’aide de deux familles de martingales nous analysons la décroissance du plus gros fragment pour des valeurs des paramètres permettant la survie du système. Cet article traite aussi de la probabilité d’extinction du processus tué.

Regenerative tree growth: structural results and convergence

We introduce regenerative tree growth processes as consistent families of random trees with n labelled leaves, n>=1, with a regenerative property at branch points. This framework includes growth processes for exchangeably labelled Markov branching trees, as well as non-exchangeable models such as the alpha-theta model, the alpha-gamma model and all restricted exchangeable models previously studied. Our main structural result is a representation of the growth rule by a sigma-finite dislocation measure kappa on the set of partitions of the natural numbers extending Bertoin's notion of exchangeable dislocation measures from the setting of homogeneous fragmentations. We use this representation to establish necessary and sufficient conditions on the growth rule under which we can apply results by Haas and Miermont for unlabelled and not necessarily consistent trees to establish self-similar random trees and residual mass processes as scaling limits. While previous studies exploited some form of exchangeability, our scaling limit results here only require a regularity condition on the convergence of asymptotic frequencies under kappa, in addition to a regular variation condition.

Consistent Markov branching trees with discrete edge lengths

We study consistent collections of random fragmentation trees with random integer-valued edge lengths. We prove several equivalent necessary and sufficient conditions under which Geometrically distributed edge lengths can be consistently assigned to a Markov branching tree. Among these conditions is a characterization by a unique probability measure, which plays a role similar to the dislocation measure for homogeneous fragmentation processes. We discuss this and other connections to previous work on Markov branching trees and homogeneous fragmentation processes.

Palindromic sequence impedes sequencing-by-ligation mechanism

BackgroundCurrent next-generation sequencing (NGS) platforms adopt two types of sequencing mechanisms: by synthesis or by ligation. The former is employed by 454 and Solexa systems, while the latter by SOLiD system. Although the pros and cons for each sequencing mechanism have more or less been discussed in a number of occasions, the potential obstacle imposed by palindromic sequences has not yet been addressed.MethodsTo test the effect of the palindromic region on sequencing efficacy, we clonally amplified a paired-end ditag sequence composed of a 24-bp palindromic sequence flanked by a pair of tags from the E. coli genome. We used the near homogeneous fragments produced from MmeI digestion of the amplified clone to generate a sequencing library for SOLiD 5500xl sequencer.ResultsResults showed that, traditional ABI sequencers, which adopt sequencing-by-synthesis mechanism, were able to read through the palindromic region. However, SOLiD 5500xl was unable to do so. Instead, the palindromic region was read as miscellaneous random sequences. Moreover, readable tag sequence turned obscure ~2 bp prior to the palindromic region.ConclusionsTaken together, we demonstrate that SOLiD machines, which employ sequencing-by-ligation mechanism, are unable to read through the palindromic region. On the other hand, sequencing-by-synthesis sequencers had no difficulty in doing so.

Homogeneous detection of cyanobacterial DNA via polymerase chain reaction

To design a primer set enabling the identification through PCR of high-quality DNA for routine and high-throughput genomic screening of a diverse range of cyanobacteria. A codon-equivalent multiple alignment of the phycocyanin alpha-subunit coding sequence (cpcA) of 22 cyanobacteria was generated and analysed to produce a single degeneracy primer set with virtually uniform product size. Also, an 18S ribosomal RNA detection set is proposed for rejecting false positives. The primer sets were tested against five diverse cyanobacteria, Chlorella vulgaris, Saccharomyces cerevisiae, and Escherichia coli. All five cyanobacteria showed positive amplification of cpcA product with homogeneous fragment length, and no products were observed for any other organism. Additionally, the only product formation observed for the 18S rRNA set was in C.vulgaris and S.cerevisiae. The newly proposed primer set served as effective check primers for cyanobacteria. Cyanobacteria gDNA had a positive, homogenous result, while other bacteria, eukaryotes and alga tested were negative. These novel, broad-spectrum primers will greatly increase the utility of PCR on newly discovered cyanobacterial species.

Current and Shot noise in DNA chains

In this paper we studied the transport properties of a finite homogeneous fragments of DNA composed by N base pairs of Guanine (poly (G)) and Cytosine (poly (C)) connected to two semi-infinite leads. We study these molecules adopting different models within a nearest neighbour tight-binding approach. We proposed a semi-analytic method for the calculation of the transport properties of DNA molecules by using Green’s function techniques within a real-space renormalization scheme. We studied the transmission probability, the I–V characteristics and the Noise power of current fluctuations as a function of intrasite and DNA-leads coupling parameters. Our results show different transport regimes for these molecular systems as a function of the coupling intensities, exhibiting metal–semiconductor transitions.

Traveling waves and homogeneous fragmentation

We formulate the notion of the classical Fisher-Kolmogorov-Petrovskii-Piscounov (FKPP) reaction diffusion equation associated with a homogeneous conservative fragmentation process and study its traveling waves. Specifically, we establish existence, uniqueness and asymptotics. In the spirit of classical works such as McKean [Comm. Pure Appl. Math. 28 (1975) 323-331] and [Comm. Pure Appl. Math. 29 (1976) 553-554], Neveu [In Seminar on Stochastic Processes (1988) 223-242 Birkh\"{a}user] and Chauvin [Ann. Probab. 19 (1991) 1195-1205], our analysis exposes the relation between traveling waves and certain additive and multiplicative martingales via laws of large numbers which have been previously studied in the context of Crump-Mode-Jagers (CMJ) processes by Nerman [Z. Wahrsch. Verw. Gebiete 57 (1981) 365-395] and in the context of fragmentation processes by Bertoin and Martinez [Adv. in Appl. Probab. 37 (2005) 553-570] and Harris, Knobloch and Kyprianou [Ann. Inst. H. Poincar\'{e} Probab. Statist. 46 (2010) 119-134]. The conclusions and methodology presented here appeal to a number of concepts coming from the theory of branching random walks and branching Brownian motion (cf. Harris [Proc. Roy. Soc. Edinburgh Sect. A 129 (1999) 503-517] and Biggins and Kyprianou [Electr. J. Probab. 10 (2005) 609-631]) showing their mathematical robustness even within the context of fragmentation theory.

Martingales and rates of presence in homogeneous fragmentations

The main focus of this work is the asymptotic behavior of mass-conservative homogeneous fragmentations. Considering the logarithm of masses makes the situation reminiscent of branching random walks. The standard approach is to study asymptotical exponential rates (Berestycki (2003) [3], Bertoin and Rouault (2005) [12]). For fixed v > 0 , either the number of fragments whose sizes at time t are of order e − v t is exponentially growing with rate C ( v ) > 0 , i.e. the rate is effective, or the probability of the presence of such fragments is exponentially decreasing with rate C ( v ) < 0 , for some concave function C . In a recent paper (Krell (2008) [21]), N. Krell considered fragments whose sizes decrease at exact exponential rates, i.e. whose sizes are confined to be of order e − v s for every s ≤ t . In that setting, she characterized the effective rates. In the present paper we continue this analysis and focus on the probabilities of presence, using the spine method and a suitable martingale. For the sake of completeness, we compare our results with those obtained in the standard approach ( [3,12]).

A phase transition for the heights of a fragmentation tree

We provide information about the asymptotic regimes for a homogeneous fragmentation of a finite set. We establish a phase transition for the asymptotic behavior of the shattering times, defined as the first instants when all the blocks of the partition process have cardinality less than a fixed integer. Our results may be applied to the study of certain random split trees. © 2010 Wiley Periodicals, Inc. Random Struct. Alg., 39, 247-274, 2011

Analysis of statistically homogeneous fragments of acoustic noises generated by insect colonies

A method of analysis of nonstationary acoustic processes was proposed. The method is based on recurrent integration, which allows tracing the basic tendencies of changes in the time structure of noise being analyzed. The method is applicable for the detection of the statistically homogeneous parts, the comparison of different parts of time series with respect to the correlation function value, and for revealing the internal diagnostic characters in nonstationary acoustic processes of different nature. The method was approved during the investigation of the relations between the changes in the physiological states of bee families and the amplitude-time-frequency structure of acoustic noise generated by them.

Branching random walks on binary search trees: convergence of the occupation measure

We consider branching random walks with binary search trees as underlying trees. We show that the occupation measure of the branching random walk, up to some scaling factors, converges weakly to a deterministic measure. The limit depends on the stable law whose domain of attraction contains the law of the increments. The existence of such stable law is our fundamental hypothesis. As a consequence, using a one-to-one correspondence between binary trees and plane trees, we give a description of the asymptotics of the profile of recursive trees. The main result is also applied to the study of the size of the fragments of some homogeneous fragmentations.

A model of the functional state of participants of laboratory markets

The dynamics of psycho-physiological characteristics of participants of laboratory markets in the process of making economical decisions in the decentralized control system is analyzed. For this purpose, the method based on the comparison of stabilographic data with the history of market actions recorded in the course of the experiment is used. The key tool for data analysis is the new segmentation algorithm, which provides efficient partitioning of the stabilographic time series into homogeneous fragments. The segmentation algorithm is obtained as the solution of the problem of estimation of the parameters of the hidden Markov model. The application of this algorithm on the level of individual decision making proves the hypothesis of connection of the stabilogram segmentation time instants of the participant with the time instants of signal actions on the laboratory market. On the level of group decisions, the effect of synchronization of stabilographic time series of participants at the time instant of auction culmination connected with revelation of private information is supported. The degree of synchronization is estimated using a proximity factor calculated based on the specially aggregated canonical correlation.

Adsorption of oxygen-containing compounds at fluorinated graphite and fluorinated carbon fiber

The surface properties of fully fluorinated samples of natural graphite (FG) and carbon fiber (FCF) were studied by gas chromatography, IR spectroscopy, and static adsorption. It was found that for fluorocarbons, the contributions from the O atom (for ethers) and the OH group (for alcohols) are comparable with the contribution from the methylene unit to the retention parameters, which is typical only of highly homogeneous, hydrophobic, and nonpolar surfaces. Unusual properties of fluorocarbons compared to known hydrophobic adsorbents include weaker adsorption of secondary alcohols than ketones, their dehydrogenation products. An analysis of the retention parameters of isomeric propanols and butanols revealed that the FCF surface is accessible to the adsorption of these molecules, and is mainly formed by planar homogeneous fragments. In contrast, the FG structure is porous; the pore width is comparable with the molecule size, which makes the adsorption equilibrium more difficult to reach.

Multifractal spectra and precise rates of decay in homogeneous fragmentations

We consider a mass-conservative fragmentation of the unit interval. Motivated by a result of Berestycki [J. Berestycki, Multifractal spectra of fragmentation processes, J. Statist. Phys. 113 (3–4) (2003) 411–430], the main purpose of this work is to specify the Hausdorff dimension of the set of locations having exactly an exponential decay. The study relies on an additive martingale which arises naturally in this setting, and a class of Lévy processes constrained to stay in a finite interval.

228. Relaxin Expression from Tumor-Targeting Adenoviruses and Its Intratumoral Spread, Apoptosis Induction, and Efficacy

Background The use of oncolytic adenoviruses as cancer gene therapy is limited by their uneven penetration and distribution in tumors. We investigated whether the expression of the cell matrix-degradative protein relaxin by adenovirus could improve adenovirus distribution and penetration in tumors. Methods We generated relaxin-expressing, replication-incompetent (dl-lacZ-RLX) and -competent (Ad-deltaE1B-RLX) adenoviruses by inserting a relaxin gene into the E3 adenoviral region. Controls were parental adenoviruses (dl-lacZ and Ad-deltaE1B) and phosphate-buffered saline (PBS) (vehicle). Replication-incompetent viruses, which do not lyse cells, were used to assess transduction efficiency. Viral spread in tumor spheroids, made by dissecting tumor tissue into homogeneous fragments, was assessed by reporter gene (i.e., lacZ) expression. Tumor growth inhibition was assessed by injecting adenoviruses into xenograft tumors in athymic mice (n = 8 or 9). Overall survival was assessed by the Kaplan-Meier method. Extracellular matrix was examined with Masson's trichrome staining. Therapeutic efficacy was evaluated by assessing spontaneous pulmonary metastasis in the B16BL6 melanoma mouse model and growth inhibition of orthotopically implanted hepatoma (n = 4-6). All statistical tests were two-sided. Results In tumor spheroids and established solid tumors in vivo, transduction with dl-lacZ-RLX, compared with parental virus or vehicle, elicited higher transduction efficiency and viral spread throughout the tumor mass. Infection with Ad-deltaE1B-RLX, compared with parental virus, elicited greater viral persistence and spread, leading to increased survival (e.g., 100%, 95% confidence interval [CI] = 63.1% to 100%, for C33A tumor-bearing mice treated with Ad-deltaE1B-RLX, and 50%, 95% CI = 15.7% to 84.3%, for C33A tumor-bearing mice treated with Ad-deltaE1B). Infection with Ad-deltaE1B-RLX substantially decreased the collagen content of tumor tissue but not of adjacent normal tissue, compared with noninfected tissues. Intratumoral injection of Ad-deltaE1B-RLX inhibited the formation of lung metastases in mice (PBS = 268 mg of metastatic tumor per mouse and Ad-deltaE1B-RLX = 10 mg; difference = 258 mg, 95% CI = 94 to 426; P = .003, Mann-Whitney test). Systemic treatment with Ad-deltaE1B-RLX completely inhibited the growth of Hep1 hepatocellular carcinomas (PBS = 20.2 mg of tumor per mouse and Ad-deltaE1B-RLX = 0 mg; difference = 20.2 mg, 95% CI = 3.7 to 36.7; P = .004, Mann-Whitney test). Conclusion Extracellular matrix degradation by relaxin expressed by adenoviruses increased viral distribution and tumor penetration, inhibited tumor growth and metastasis, and increased survival of mice.

Chord length analysis of the fragments of a ‘dead leaves’ tessellation

Let the (homogeneous) fragments of a puzzle, resulting from a ‘dead leaves’ tessellation, be embedded in a homogeneous medium (constant density). The application of elastic scattering methods allows the determination of second-order characteristics and derived functions of these particles (set covariance, geometric covariogram, chord length distribution). The second-order characteristics of the grains of the ‘dead leaves’ model, closely interrelated with those of the resulting tessellation pieces, can be considered as puzzle particles (PPs). A discussion of the behaviour of the chord length distribution of the PPs allows the origin of the shape of the PPs to be characterized. For fitting PPs, the mean small-angle scattering correlation function γ P (r) of the PPs fulfills γ P ″(0)/[γ P ′ (0)]2 = 1.

Relaxin Expression From Tumor-Targeting Adenoviruses and Its Intratumoral Spread, Apoptosis Induction, and Efficacy

The use of oncolytic adenoviruses as cancer gene therapy is limited by their uneven penetration and distribution in tumors. We investigated whether the expression of the cell matrix-degradative protein relaxin by adenovirus could improve adenovirus distribution and penetration in tumors. We generated relaxin-expressing, replication-incompetent (dl-lacZ-RLX) and -competent (Ad-deltaE1B-RLX) adenoviruses by inserting a relaxin gene into the E3 adenoviral region. Controls were parental adenoviruses (dl-lacZ and Ad-deltaE1B) and phosphate-buffered saline (PBS) (vehicle). Replication-incompetent viruses, which do not lyse cells, were used to assess transduction efficiency. Viral spread in tumor spheroids, made by dissecting tumor tissue into homogeneous fragments, was assessed by reporter gene (i.e., lacZ) expression. Tumor growth inhibition was assessed by injecting adenoviruses into xenograft tumors in athymic mice (n = 8 or 9). Overall survival was assessed by the Kaplan-Meier method. Extracellular matrix was examined with Masson's trichrome staining. Therapeutic efficacy was evaluated by assessing spontaneous pulmonary metastasis in the B16BL6 melanoma mouse model and growth inhibition of orthotopically implanted hepatoma (n = 4-6). All statistical tests were two-sided. In tumor spheroids and established solid tumors in vivo, transduction with dl-lacZ-RLX, compared with parental virus or vehicle, elicited higher transduction efficiency and viral spread throughout the tumor mass. Infection with Ad-deltaE1B-RLX, compared with parental virus, elicited greater viral persistence and spread, leading to increased survival (e.g., 100%, 95% confidence interval [CI] = 63.1% to 100%, for C33A tumor-bearing mice treated with Ad-deltaE1B-RLX, and 50%, 95% CI = 15.7% to 84.3%, for C33A tumor-bearing mice treated with Ad-deltaE1B). Infection with Ad-deltaE1B-RLX substantially decreased the collagen content of tumor tissue but not of adjacent normal tissue, compared with noninfected tissues. Intratumoral injection of Ad-deltaE1B-RLX inhibited the formation of lung metastases in mice (PBS = 268 mg of metastatic tumor per mouse and Ad-deltaE1B-RLX = 10 mg; difference = 258 mg, 95% CI = 94 to 426; P = .003, Mann-Whitney test). Systemic treatment with Ad-deltaE1B-RLX completely inhibited the growth of Hep1 hepatocellular carcinomas (PBS = 20.2 mg of tumor per mouse and Ad-deltaE1B-RLX = 0 mg; difference = 20.2 mg, 95% CI = 3.7 to 36.7; P = .004, Mann-Whitney test). Extracellular matrix degradation by relaxin expressed by adenoviruses increased viral distribution and tumor penetration, inhibited tumor growth and metastasis, and increased survival of mice.

Solar wind polytropic index estimates based on single spacecraft plasma and interplanetary magnetic field measurements

We propose an approach for estimating the polytropic index in the solar wind. This is an artificially introduced parameter simplifying essentially the gasdynamic or magnetogasdynamic modeling of the interplanetary plasma. The problem in the straightforward utilization of the polytropic equation is to find sufficient homogeneous fragments of the solar wind flow, observed by single spacecraft only, where the application of this polytropic equation is correct. We propose an algorithm for following the plasma data time series to ensure the separation of data segments that belong, with high probability, to the same plasma flow flux tube. A linear regression model between logarithms of plasma density and temperature within such a segment provides an estimate for the polytropic index. Some preliminary applications of the algorithm to real data from spacecraft crossings of different solar wind structures are performed for the Bastille event of 14–16 July 2000.