Number Of Dynamic Processes Research Articles

Dynamic regimes of the Greenland Ice Sheet emerging from interacting melt–elevation and glacial isostatic adjustment feedbacks

Abstract. The stability of the Greenland Ice Sheet under global warming is governed by a number of dynamic processes and interacting feedback mechanisms in the ice sheet, atmosphere and solid Earth. Here we study the long-term effects due to the interplay of the competing melt–elevation and glacial isostatic adjustment (GIA) feedbacks for different temperature step forcing experiments with a coupled ice-sheet and solid-Earth model. Our model results show that for warming levels above 2 ∘C, Greenland could become essentially ice-free within several millennia, mainly as a result of surface melting and acceleration of ice flow. These ice losses are mitigated, however, in some cases with strong GIA feedback even promoting an incomplete recovery of the Greenland ice volume. We further explore the full-factorial parameter space determining the relative strengths of the two feedbacks: our findings suggest distinct dynamic regimes of the Greenland Ice Sheets on the route to destabilization under global warming – from incomplete recovery, via quasi-periodic oscillations in ice volume to ice-sheet collapse. In the incomplete recovery regime, the initial ice loss due to warming is essentially reversed within 50 000 years, and the ice volume stabilizes at 61 %–93 % of the present-day volume. For certain combinations of temperature increase, atmospheric lapse rate and mantle viscosity, the interaction of the GIA feedback and the melt–elevation feedback leads to self-sustained, long-term oscillations in ice-sheet volume with oscillation periods between 74 000 and over 300 000 years and oscillation amplitudes between 15 %–70 % of present-day ice volume. This oscillatory regime reveals a possible mode of internal climatic variability in the Earth system on timescales on the order of 100 000 years that may be excited by or synchronized with orbital forcing or interact with glacial cycles and other slow modes of variability. Our findings are not meant as scenario-based near-term projections of ice losses but rather providing insight into of the feedback loops governing the “deep future” and, thus, long-term resilience of the Greenland Ice Sheet.

Туризм та рекреація в сільській місцевості: проблема кластерного підходу

This study examines modern rural changes associated with the transition from an economy focused on production to an economy focused on services, which in the future will allow the formation of tourist clusters within rural areas. The history of the formation of a scientific view on such concepts as "rural", "rural area", "rural tourism and recreation" is studied. Three main characteristics that clearly define the districts as rural were studied: population density and size of the settlement, land use and economy, traditional public structures. The spectrum of tourist and recreational activities in the countryside has been formed, which make up its attractiveness through attractions and the development of relevant types of tourism. The potential aspects of the development of rural tourism are identified. An analysis of socio-economic, cultural, and physical influences on the development of tourism and recreation in rural areas was proposed. A number of dynamic processes in the measurement of world trends are highlighted. The general strategy of the tourist cluster is proposed.

Forecast of power generation and heat production from renewable energy sources

The share of renewable energy sources (RES) in the end use of energy in the UE will increase from the present level of about 25% to 50 % in 2030 according to the assumptions of the European Commission. In Poland the RES Act was passed in 2015. The act defines mechanisms and instruments for supporting the production of electricity and heat from renewable energy sources. Statistics (2003–2014) of electricity generation and heat production from RES in Poland were used in the research. Because of amendments to regulations connected with promoting RES and the emissions trading system (ETS) as well as the uncertainty associated with further directions of the energy and environmental policy, generation of electricity and heat based on the use of RES must be modelled while taking risk into account. A number of dynamic processes incorporating random events may be modelled by stochastic equations using Ito calculus. By applying Euler’s method to solve stochastic differential equations (SDE), it is possible to simulate the development of the use of renewable energy carriers in electricity generation and heat production in the future.

Mechanistic Models of Chemical Exchange Induced Relaxation in Protein NMR.

Long-lived conformational states and their interconversion rates critically determine protein function and regulation. When these states have distinct chemical shifts, the measurement of relaxation by NMR may provide us with useful information about their structure, kinetics, and thermodynamics at atomic resolution. However, as these experimental data are sensitive to many structural and dynamic effects, their interpretation with phenomenological models is challenging, even if only a few metastable states are involved. Consequently, approximations and simplifications must often be used which increase the risk of missing important microscopic features hidden in the data. Here, we show how molecular dynamics simulations analyzed through Markov state models and the related hidden Markov state models may be used to establish mechanistic models that provide a microscopic interpretation of NMR relaxation data. Using ubiquitin and BPTI as examples, we demonstrate how the approach allows us to dissect experimental data into a number of dynamic processes between metastable states. Such a microscopic view may greatly facilitate the mechanistic interpretation of experimental data and serve as a next-generation method for the validation of molecular mechanics force fields and chemical shift prediction algorithms.

ON THE UNUSUAL GAS COMPOSITION IN THE β PICTORIS DEBRIS DISK

The metallic gas associated with the Beta Pic debris disk is not believed to be primordial, but arises from the destruction of dust grains. Recent observations have shown that carbon and oxygen in this gas are exceptionally overabundant compared to other elements, by some 400 times. We study the origin of this enrichment under two opposing hypothesis, preferential production, where the gas is produced with the observed unusual abundance (as may happen if gas is produced by photo-desorption from C/O-rich icy grains), and preferential depletion, where the gas evolves to the observed state from an original solar abundance (if outgassing occurs under high-speed collisions) under a number of dynamical processes. We include ... ... We find ... ...

On turbulent fragmentation and the origin of the stellar IMF

Two varieties of the universal stellar initial mass function (IMF) viz., the Kroupa and the Chabrier IMF, have emerged over the last decade to explain the observed distribution of stellar masses. The possibility of the universal nature of the stellar IMF leads us to the interesting prospect of a universal mode of star-formation. It is well-known that turbulent fragmentation of gas in the interstellar medium produces a lognormal distribution of density which is further reflected by the mass-function for clumps at low and intermediate masses. Stars condense out of unstable clumps through a complex interplay between a number of dynamic processes which must be accounted for when tracing the origin of the stellar IMF. In the present work, applying the theory of gravitational fragmentation we first derive the mass function (MF) for clumps. Then a core mass function (CMF) is derived by allowing the clumps to fragment, having subjected each one to a random choice of gas temperature. Finally, the stellar IMF is derived by applying a random core-to-star conversion efficiency, ϵ, in the range of 5–15% to each CMF. We obtain a power-law IMF that has exponents within the error-bars on the Kropua IMF. This derived IMF is preceded by a similar core mass function which suggests, gravoturbulent fragmentation plays a key role in assembling necessary conditions that relate the two mass-functions. In this sense the star-formation process, at least at low redshifts where gas cooling is efficient, is likely to be universal. We argue that the observed knee in the CMF and the stellar IMF may alternatively be interpreted in terms of the characteristic temperature at which gas in potential star-forming clouds is likely to be found. Our results also show that turbulence in star-forming clouds is probably driven on large spatial scales with a power-spectrum steeper than Kolmogorov-type.

Dynamics of memory: Commemorating the 2005 London bombings in British television news

This article seeks to examine coverage of the 2005 London bombings’ first year anniversary commemorations vis-à-vis reportage of the attacks as a breaking news story. Adopting a multimodal discourse analysis approach, informed by both qualitative and quantitative methods, the study explores the thematic relationship between the two sets of coverage. Although our results show a number of dynamic processes at work, a key finding is the strong tendency for new themes to appear in the commemorative story. Our analyses also highlight the cathartic function that the event’s anniversary itself seemingly fulfils. Such empirical insights have important implications for the ways in which (catastrophic) past events are commemorated through the mass media, especially through the medium of television.

Cuboidal Mo3S4 and Mo3NiS4 Complexes Bearing Dithiophosphates and Chiral Carboxylate Ligands: Synthesis, Crystal Structure and Fluxionality

AbstractNew triangular Mo and W cluster complexes incorporating (S)‐lactic acid (HLac), [Mo3S4(μ‐Lac)(dtp)3(py)] (1) and [W3S4(μ‐Lac)(dtp)3(py)] (2), were prepared [dtp = (EtO)2PS2]. Analogous synthetic procedures were adapted for the synthesis of cuboidal Mo3NiS4 to yield [Mo3(Nipy)S4(py)(μ‐OAc)(dtp)3(py)] (3). The crystal structures of 1 and 3 were determined. A detailed variable‐temperature 31P{1H} and 1H NMR study of compounds 1 and 3 indicated fluxional behaviour in non‐coordinating solvents (CDCl3, CD2Cl2 and CDCl2CDCl2). A number of dynamic processes were identified involving the Mo–py site that include configuration inversion [(P) to (M)], hindered Mo–N rotation and pyridine exchange. Experiments with deuterated pyridine revealed a faster substitutional lability of Mo–py compared with Ni–py.

Recruitment of heterochromatin protein 1 to DNA repair sites

Heterochromatin protein 1 (HP1) was originally identified as a constitutive component of heterochromatin. However it is recognized now that it plays an important role in a number of dynamic processes in the cell nucleus, including transcriptional repression and regulation of euchromatic genes. Recent reports demonstrate that HP1 may be involved in the DNA damage response. Two seemingly contradictory phenomena have been observed-HP1 detachment from chromatin and HP1 recruitment to damaged DNA foci. Based on quantitative FRAP and FLIP studies carefully designed to minimize phototoxicity, we demonstrate that HP1 is recruited to the damaged regions in hetero- as well as euchromatin within a few minutes after damage.

Efficient dependency tracking for relevant events in concurrent systems

In a concurrent system with N processes, vector clocks of size N are used for tracking dependencies between the events. Using vectors of size N leads to scalability problems. Moreover, association of components with processes makes vector clocks cumbersome and inefficient for systems with a dynamic number of processes. We present a class of logical clock algorithms, called chain clock, for tracking dependencies between relevant events based on generalizing a process to any chain in the computation poset. Chain clocks are generally able to track dependencies using fewer than N components and also adapt automatically to systems with dynamic number of processes. We compared the performance of Dynamic Chain Clock (DCC) with vector clock for multithreaded programs in Java. With 1% of total events being relevant events, DCC requires 10 times fewer components than vector clock and the timestamp traces are smaller by a factor of 100. For the same case, although DCC requires shared data structures, it is still 10 times faster than vector clock in our experiments. We also study the class of chain clocks which perform optimally for posets of small width and show that a single algorithm cannot perform optimally for posets of small width as well as large width.

Calculation of Photon-Count Number Distributions via Master Equations

Fitting of photon-count number histograms is a way of analysis of fluorescence intensity fluctuations, a successor to fluorescence correlation spectroscopy. First versions of the theory for calculating photon-count number distributions have assumed constant emission intensity by a molecule during a counting time interval. For a long time a question has remained unanswered: to what extent is this assumption violated in experiments? Here we present a theory of photon-count number distributions that takes account of intensity fluctuations during a counting time interval. Theoretical count-number distributions are calculated via a numerical solution of Master equations (ME), which is a set of differential equations describing diffusion, singlet-triplet transitions, and photon emission. Detector afterpulsing and dead-time corrections are also included. The ME-theory is tested by fitting a series of photon-count number histograms corresponding to different lengths of the counting time interval. Compared to the first version of fluorescence intensity multiple distribution analysis theory introduced in 2000, the fit quality is significantly improved. It is discussed how a theory of photon-count number distributions, which assumes constant emission intensity during a counting time interval, may also yield a good fit quality. We argue that the spatial brightness distribution used in calculations of the fit curve is not the true spatial brightness distribution. Instead, a number of dynamic processes, which cause fluorescence intensity fluctuations, are indirectly taken into account via the profile adjustment parameters.

The programming language superpascal

AbstractThis paper defines SuperPascal—a secure programming language for publication of parallel scientific algorithms. SuperPascal extends a subset of IEEE Standard Pascal with deterministic statements for parallel processes and synchronous message communication. A parallel statement denotes parallel execution of a fixed number of statements. A forall statement denotes parallel execution of the same statement by a dynamic number of processes. Recursive procedures may be combined with parallel and forall statements to define recursive parallel processes. Parallel processes communicate by sending typed messages through channels created dynamically. SuperPascal omits ambiguous and insecure features of Pascal. Restrictions on the use of variables enable a single‐pass compiler to check that parallel processes are disjoint, even if the processes use procedures with global variables.

A molecular dynamics method for obtaining the vibrational spectra of macromolecules

A molecular dynamics-based method is used to compute the vibrational spectra and dispersion curves of a polyethylene chain. The results are compared and contrasted with those of normal mode calculations, demonstrating the validity of the approach and providing fundamental insight into a number of dynamical processes. The strength of the method is its computational efficiency and that it represents an exact classical dynamics approach to calculating vibrational spectra, thereby eliminating many of the weaknesses of normal mode calculations (i.e., the harmonic approximation).

A time-of-flight spectrometer for low-energy neutral and ionized alkalis

A time-of-flight spectrometer has been developed for measuring velocity- and angle-resolved distributions of neutral and ionized alkali atoms in the range of several electron volts to several thousand electron volts. The spectrometer is mounted on a rotating platform inside a previously existing ultra-high-vacuum scattering chamber equipped with a low-energy ion beamline. A high work function platinum foil, placed after a pair of angle-defining apertures, is used to ionize the alkali atoms, regardless of their incident charge states. After striking the platinum foil, the alkali ions are accelerated and detected with a channel electron multiplier. Velocity resolution of the scattered flux is achieved using standard time-of-flight techniques. Neutral and ionized alkali atoms are detected with the same high efficiency. The ion flux can be rejected by biasing a pair of rejection elements, and therefore absolute ratios of the neutral to total flux can be determined. Such a spectrometer can be used to probe the role of charge transfer in a number of dynamical processes at surfaces.

Programming divide and conquer for a mimd machine

AbstractThis paper discusses our efforts in implementing a divide and conquer algorithm (adaptive quadrature) on the HEP computer system. The one PEM HEP system performs in a MIMD fashion by pipelining execution of instructions from different processes. Unlike most divide and conquer approaches, our strategy ensures that the program will never deadlock due to memory expansion or spawning too many processes. Within this constraint we develop and analyse two different implementations: one using a static number of processes and the other a dynamic number of processes. Our results examine the relative performance of these two schemes. In addition we briefly discuss some of our impressions concerning some ‘myths of parallel programming’.

Zonation in the marsh vegetation of the Blackwood River Estuary in south-western Australia

There is little published information about coastal salt marshes in south-western Australia, which are prominent in estuaries but absent from the high energy coastline. The zonation of the marshes of the Blackwood estuary resemble those in other parts of the world, in that Sarcocornia marsh occurs near the mouth, followed by rush marsh, with sedges further upstream, suggesting that salinity is a prime determining factor. Spartina and Phragmites are absent. The most exensive marsh is the Juncus kraussii rush community which is invaded by the paperbark tree, Melaleuca cuticularis. The sedge Baumea juncea forms a marsh community on the shores of the lower tidal river and a progression of species occurs with distance along the tidal river. A number of dynamic processes observed in these marshes are described and related to observations elsewhere