Pair Formation Process Research Articles

Minimal Cooling of Neutron Stars: A New Paradigm

A new classification of neutron star cooling scenarios, involving either ``minimal'' cooling or ``enhanced'' cooling is proposed. The minimal cooling scenario replaces and extends the so-called standard cooling scenario to include neutrino emission from the Cooper pair breaking and formation process. This emission dominates that due to the modified Urca process for temperatures close to the critical temperature for superfluid pairing. Minimal cooling is distinguished from enhanced cooling by the absence of neutrino emission from any direct Urca process, due either to nucleons or to exotica. Within the minimal cooling scenario, theoretical cooling models can be considered to be a four parameter family involving the equation of state of dense matter, superfluid properties of dense matter, the composition of the neutron star envelope, and the mass of the neutron star. Consequences of minimal cooling are explored through extensive variations of these parameters. Results are compared with the inferred properties of thermally-emitting neutron stars in order to ascertain if enhanced cooling occurs in any of them. All stars for which thermal emissions have been clearly detected are at least marginally consistent with the lack of enhanced cooling. The two pulsars PSR 0833-45 (Vela) and PSR 1706-44 would require enhanced cooling in case their ages and/or temperatures are on the lower side of their estimated values whereas the four stars PSR 0656+14, PSR 1055-52, Geminga, and RX J0720.4-3125 may require some source of internal heating in case their age and/or luminosity are on the upper side of their estimated values. The new upper limits on the thermal luminosity of PSR J0205+6449 and RX J0007.0+7302 are indicative of the occurrence of some enhanced neutrino emission beyond the minimal scenario.

On pair and tuple formation under independent Poisson or renewal arrival processes

We present several results refining and extending those of Neuts and Alfa on weak convergence of the pair-formation process when arrivals follow two independent Poisson processes. Our results are obtained using a different, more straightforward, and apparently simpler probabilistic approach. Firstly, we give a very short proof of the fact that the convergence of the pair-formation process to a Poisson process actually holds in total variation (with a bound for convergence rate). Secondly, we extend the result of the theorem to the case of multiple labels: there are d independent arrival Poisson processes, and we are looking at the epochs when d-tuples are formed. Thirdly, we extend the original (weak convergence) result to the case when arrivals follow independent renewal processes (this extension is also valid for the d-tuple formation).

On pair and tuple formation under independent Poisson or renewal arrival processes

We present several results refining and extending those of Neuts and Alfa on weak convergence of the pair-formation process when arrivals follow two independent Poisson processes. Our results are obtained using a different, more straightforward, and apparently simpler probabilistic approach. Firstly, we give a very short proof of the fact that the convergence of the pair-formation process to a Poisson process actually holds in total variation (with a bound for convergence rate). Secondly, we extend the result of the theorem to the case of multiple labels: there are d independent arrival Poisson processes, and we are looking at the epochs when d-tuples are formed. Thirdly, we extend the original (weak convergence) result to the case when arrivals follow independent renewal processes (this extension is also valid for the d-tuple formation).

Pair formation in a Markovian arrival process with two event labels

The stochastic process resulting when pairs of events are formed from two point processes is a rich source of questions. When the two point processes have different rates, the resulting stochastic process has a mean drift towards either -∞ or +∞. However, when the two processes have equal rates, we end up with a null-recurrent Markov chain and this has interesting behavior. We study this process for both discrete and continuous times and consider special cases with applications in communications networks. One interesting result for applications is the waiting time of a packet waiting for a token, a special case of this pair-formation process. Pair formation by two independent Poisson processes of equal rates results in a point process that is asymptotically a Poisson process of the same rate.

Pair formation in a Markovian arrival process with two event labels

The stochastic process resulting when pairs of events are formed from two point processes is a rich source of questions. When the two point processes have different rates, the resulting stochastic process has a mean drift towards either -∞ or +∞. However, when the two processes have equal rates, we end up with a null-recurrent Markov chain and this has interesting behavior. We study this process for both discrete and continuous times and consider special cases with applications in communications networks. One interesting result for applications is the waiting time of a packet waiting for a token, a special case of this pair-formation process. Pair formation by two independent Poisson processes of equal rates results in a point process that is asymptotically a Poisson process of the same rate.

Interaction of L-tartaric acid with alkaline metals and open chain polyammonium cations in aqueous solution

The interaction of L-tartrate with alkaline metal ions was studied by potentiometry and ultraviolet circular dichroism (UV/CD), and the formation of L-tartrate–polyammonium cation species was also studied by calorimetry. The ultraviolet circular dichroism technique was also used in order to clarify some aspects of the ion pair formation process between L-tartrate anion and alkaline (various ionic strength values were employed) or polyammonium cations. As in potentiometry, tetraethylammonium chloride has been considered as a reference ionic medium (that is, used as a non-interactive salt) for each comparison of the CD spectra recorded in different solutions. The spectropolarimetric technique was shown to be an efficient means of establishing the capacity of the ions considered for mutual conformational adaptability. Some differences clearly appear between the ion pairs formed by L-malate, studied in a previous paper, and L-tartrate anions. In the systems L-tartrate–polyammonium cations the species ALHr are formed [L = tartrate, A = amine, r = 1, 2, …, (n + 1), n = maximum protonation degree of amine] with stability depending on the charges involved in the formation reaction. Comparisons are made with other carboxylic ligands previously investigated.

SIZE-ASSORTATIVE PAIRING IN THE BIG-CLAWED SNAPPING SHRIMP, ALPHEUS HETEROCHELIS

Abstract The big-clawed snapping shrimp, Alpheus heterochelis, is found in size-matched male-female pairs. A common assumption is that a large size advantage in males, an extended pair bond, and a positive correlation between female size and fecundity promotes size-assortative pairing. Since all of these conditions apply to A. heterochelis, we investigated size-assortative pairing in the laboratory by designing experiments in which the pairs were size matched or mismatched using three size categories; large, medium and small. We found that snapping shrimps prefer to pair according to size and that such pairing is stable. We also found that, contrary to the initial assumptions, female-female competition and female choice for large males plays the main role in the pair formation process. Smaller, and hence less competitively successful, females will pair with smaller males, but in a male-biased environment, will preferentially pair with larger males. Large males provide the best protection from shelter eviction, which is crucial for female A. heterochelis, as their reproduction is closely associated with moult, and therefore requires shelter and a male present for successful reproduction.

Neutral C60 effusive source for atomic collisions with fullerene

A neutral C60 effusive source was assembled in a crossed molecular-beam apparatus in order to perform atom–molecule electron transfer collisions and its calibration by time-of-flight mass spectrometry. This source consists of a stainless-steel oven where the C60 sublimation takes place. Typical operation temperatures are in the range of 723 up to 888 K. Through this setup the study of the ion pair formation process K+C60→K++C60− (where K is a potassium atom) can be performed in a wide range of collision energies (10 up to 500 eV). The results show evidence of negative ion formation (being the ratio of intensities between the parent ion and fragment ions) clearly dependent on the collision energy used.

Modeling and Simulation for Microelectronic Materials Research

Recent development in modeling and simulation for microelectronic materials research in the areas of Cu alloy interconnect is presented. A model for defect generation and diffusion through a Frenkel pair formation process at grain boundaries under electromigration conditions was developed. The model has consistently predicted the activation energies well for all the interconnect materials, namely Al, Al-Cu, Cu, and Cu alloys. A virtual simulation procedure was developed to screen a beneficial dopant to Cu based on the assumption that grain boundary (GB) diffusion dominantly controls the electromigration performance. The procedure covers dopant segregation to GB, dopant bulk diffusion, dopant and Cu diffusion along GB, and the effect of presence of a dopant on Cu diffusion at GB by dragging and blocking (stuffing) mechanisms. The success of the procedure has convincingly shown that modeling and simulation is the first choice to design advanced materials systems for next generation of interconnect.

Deterministic approximations for stochastic processes in population biology

Differential equations are frequently used as deterministic models for stochastic processes. They approximate the expectations of the modeled stochastic processes, and are presumably good approximations when the state space (population) is sufficiently large. Although experimental simulations often support this approach, the justification of the use of deterministic equations for describing stochastic processes is not obvious. Some examples show that the deterministic approximation can deviate considerably from the exact result even for large populations. In this paper, we study two model examples: (a) A one sex pair formation process occurring in a closed population, with a nonlinear transition rate that results from assuming the mass action law for the pairing rule. This process has a finite state space. (b) A one sex pair formation process obtained from the first scenario by adding the effects of immigration and death. This process has an infinite state space. For both scenarios we compute analytically the equilibrium behavior of the stochastic and the deterministic models. We use these computations to compare the equilibrium expectations (in the infinite case) and the asymptotic expansions of the equilibrium expectations (in the finite state space model) of the stochastic processes with their deterministic counterparts. We use this comparison to study the appropriate representation of the mass action type reactions, and to study the quality of the deterministic model as an approximation for the stochastic scenario.

Determination of the pre-exponential factor and the activation energy for the low-temperature dislocation relaxation in aluminum

The ultrasonic attenuation and the sound velocity at 10 MHz were measured in deformed Al single crystals in the temperature range between 1.5 and 50 K. In the high purity specimen (RRR=20 000) the change in sound velocity due to deformation shows a step in temperature dependence at 17 K, which corresponds to the 11 K relaxation peak at 50 kHz found by Kosugi and Kino [J. Phys. Soc. Jpn. 58 (1989) 4269], although the change in attenuation due to deformation was masked by the large background attenuation due to phonon–electron interaction. From the present experiment and that of Kosugi and Kino, the activation energy and the attack frequency of the relaxation process are estimated to be 14 meV and 1.0×10 12/s, respectively. If the kink pair formation process of dislocations on the Peierls potential is responsible for this relaxation, the Peierls stress is 5.4×10 −5 G, where G is the shear modulus, and this value does not conflict with the flow stress at low temperatures.

Thermally Activated Motion of a Screw Dislocation Overcoming the Peierls Potential for Prismatic Slip in an hcp Lattice

The prismatic slip in hcp metals has been studied by calculating the thermally activated motion of a 1/3[1120] screw dislocation in a two-dimensional Peierls potential assumed in the (1120) plane. The kink pair formation process for the transition of the dislocation from a stable position to another under applied stress has been investigated and the activation energies for the two types of transitions constituting the prismatic slip have been calculated. Using the activation energies, the critical flow stress τc has been deduced as a function of the direction of the applied stress χ and temperature. The calculated τc–χ relations deviate significantly from the Schmid law and well reproduce the deviation relation observed in the experimental data of Ti. The deviation from the Schmid law originates in a structural feature of the hcp lattice itself, i.e., a zigzag arrangement along the prismatic plane of atomic rows.

Intra- and Intersexual Functions in the Call, of a Non-Passerine Bird

Abstract The thin-billed prion Pachyptila belcheri is a long-lived, monogamous and nocturnal seabird breeding in burrows in dense colonies in the southern hemisphere. Like all other Procellariiformes, this species shows delayed sexual maturity, and pair formation takes several years of active courtship. Its mating behaviour nearly exclusively relies on vocal cues. Its call is strongly sexually dimorphic. In this paper, we examine intra- and intersexual functions of call, and test whether these functions vary according to (1) the status of the recipient birds (breeding versus non breeding), and (2) the stage of pair formation. We used specifically designed playback experiments as three successive stages of the pair formation are recognized (stage 1: male and female in flight, stage 2: male on ground and female in flight and stage 3: male and female on ground). The first set of playback experiments was performed outside breeding colonies (stage 1). We found that wandering non-breeders (i.e. young birds which have still to find a partner) were strongly attracted and caught in mist nets when playback calls of both sexes were used. Conversely, breeders significantly avoided playback. Playback of male calls caught slightly more non-breeding females than did female calls, the reverse also being true. However, capture rates (i.e. number of birds caught per time unit) did not differ according to the sex of the call played-back. Thus, at the earliest stage of pair formation, wandering non-breeders of both sexes are attracted by their species-specific call, regardless of the sex of the call. The second set of experiments was performed on the breeding colonies and was aimed at testing the response of birds in flight (stage 2). Playback of male calls resulted in a significant increase of the vocal activity of flying females as well as a decrease of flying males calling activity. Playback of female calls had no detectable effects. Thus, at this stage of the pair formation process, birds do take into account the sexual information that is encoded within the call, and react according to their sex. The third set of tests was addressed to birds within their burrows (stage 3). We found that breeding birds responded far more to the calls of their own sex, remaining silent to those of the opposite sex: birds took into account the sexual information, but in a reverse sense compared to stage 2. Conversely, non-breeders occupying burrows responded more often to birds of the opposite sex. Our results therefore showed that the same signal can be used in intra- and intersexual communication, depending on the status of the signaller (its sex) and of the recipient (its sex and breeding status).

Modeling Prevention Strategies for Gonorrhea and Chlamydia Using Stochastic Network Simulations

A simulation model was used to study the spread of two sexually transmitted diseases (STDs), namely gonorrhea and genital infection with Chlamydia trachomatis. The model is based on a stochastic pair formation and separation process, which describes the underlying structure of the sexual contact pattern. It is implemented as a Monte Carlo simulation model. Spread of the STDs was modeled in an age-structured heterosexual population with a highly sexually active core group. Contact tracing strategies, screening of various subgroups, and the effect of condom use were compared. The authors conclude that contact tracing is very effective as a prevention strategy, that screening should be targeted to the highly active core group, that age is not sufficient as a determinant for high sexual activity to make screening of certain age groups useful, and, finally, that consistent condom use by a fraction of the population can contribute substantially to the prevention of STDs. All strategies proved more effective for gonorrhea than for Chlamydia prevention, which may explain the relatively high prevalence of Chlamydia found in many heterosexual populations.

A network modelling approach for assessing the efficiency of prevention strategies

Survey data and a simulation model based on a stochastic pair formation process are used to construct networks of sexual contacts. We model heterosexual partnerships which can be steady or casual depending on their average duration. Transmission of an infectious disease can take place in pairs of a susceptible and an infected individual. We study networks of sexual contacts accumulated during 1 year for different types of mixing patterns. The networks are constructed on the basis of data from a survey in The Netherlands. We analyze the network structure for different mixing patterns and investigate the relationship between network structure and disease spread; furthermore we study the effect of prevention measures on the structure of the network.

Kink Pair Formation Process on Screw Dislocations in BCC Metals

Kink Pair Formation Process on Screw Dislocations in BCC Metals

Anelastic study of screw-dislocation motion in high-purity tantalum

The kink pair formation (KPF) process on screw dislocations in Ta was investigated by means of the anelastic creep (AEC) measurements near room temperature. The effect of σ eff on H KPF and that on ν 0 were investigated for σ eff below 16 MPa, where σ eff denotes the effective stress applied to screw dislocations responsible for the AEC through KPF, H KPF the activation enthalpy of the KPF process, and ν 0 the pre-exponential factor of the inverse of the relaxation time of the KPF process. The extrapolation of the observed σ eff dependence gives 2 H k = 0.97 ± 0.03 eV and In[ ν 0,0(s −1)] = 29.6 ± 1, where H k denotes the enthalpy of an isolated single kink and ν 0.0 is ν 0 at σ eff = 0. Both H KPF and ν 0 show a strong decrease with increasing σ eff. These features for H KPF and ν 0 are very similar to those reported for Nb and Fe after the AEC measurements. We surmise that a change in the core structure of screw dislocation plays an important role for the rate of KPF on screw dislocations in the b.c.c. metals. The AEC results are discussed together with the strong decrease in H KPF with increasing σ eff reported for Fe, Nb and Ta after the flow stress measurements.

Donor-Acceptor Pairs in Silicon

ABSTRACTStable forms of donor-acceptor pairs in silicon arise from the interaction between negatively charged acceptors and 3d transition element donors, which, occupying interstitial sites, have high mobilities. The atomic and electronic structure of these pairs can be studied in detail by magnetic resonance. The symmetry of centers as observed in the resonance experiments gives strict constraints on the applicable atomic models. The spin of centers is related to their charge state. Hyperfine interactions frequently lead to a specific structure in the spectra, which characterizes the chemical identity of atomic components of the pair. Deep level transient spectroscopy provides a way of sensitive observation of electrically active impurities: to determine their concentrations and associated electronic levels. It allows the study of the kinetics of the pair formation process and thermally induced dissociation; binding energies can be determined. Transformation of pairs as a result of illumination was also observed. Several of the pairs can exist in geometrically different atomic configurations leading to the phenomenon of bi- or multi-stability. In the paper the donor-acceptor pair formation process is illustrated by examples involving the substitutional double acceptor zinc, for which new data became recently available.

Femtosecond-picosecond laser photolysis studies of the ion pair formation process in the excited state of the charge-transfer complex in solution

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTFemtosecond-picosecond laser photolysis studies of the ion pair formation process in the excited state of the charge-transfer complex in solutionHiroshi Miyasaka, Seishi Ojima, and Noboru MatagaCite this: J. Phys. Chem. 1989, 93, 9, 3380–3382Publication Date (Print):May 1, 1989Publication History Published online1 May 2002Published inissue 1 May 1989https://doi.org/10.1021/j100346a003RIGHTS & PERMISSIONSArticle Views216Altmetric-Citations53LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (401 KB) Get e-Alerts

Pair formation in age-structured populations.

In population theory birth and death can be modeled, to a certain extent, by linear equations, but the formation of pairs is a nonlinear phenomenon. Separation of pairs can again be described by linear equations. In particular in human demography it is a long-standing problem by what type of equation pair formation shall be described, in other words, to find an appropriate marriage function. From the work of Kendall (1949), Keyfitz (1972), McFarland (1972), Parlett (1972), Pollard (1973), Fredrickson (1971), Staroverov (1977), Pollak (1987) it is quite clear that mass action kinetics is not appropriate, the marriage law must be homogeneous of degree one. Several special laws have been proposed, e.g. the harmonic mean and the minimum law, but there seems to be no law which is rigorously derived from a microscopic description of the pair formation process. On the other hand ist is obvious what the general properties of a marriage function should be (Fredrickson 1971, see properties 1), 2), 3) below). For such functions we derive a theory of pair formation, that continues and in some sense completes earlier work on this topic. In (Hadeler et al. 1988) we have developed an approach to homogeneous evolution equations, and this theory provides the appropriate framework for pair formation models. In fact we have given a complete analysis of the existence conditions for equilibria and of the global stability problem for these models, for continuous time and in the absence of age structure.