1,416 research outputs found
Time After Time: Notes on Delays In Spiking Neural P Systems
Spiking Neural P systems, SNP systems for short, are biologically inspired
computing devices based on how neurons perform computations. SNP systems use
only one type of symbol, the spike, in the computations. Information is encoded
in the time differences of spikes or the multiplicity of spikes produced at
certain times. SNP systems with delays (associated with rules) and those
without delays are two of several Turing complete SNP system variants in
literature. In this work we investigate how restricted forms of SNP systems
with delays can be simulated by SNP systems without delays. We show the
simulations for the following spike routing constructs: sequential, iteration,
join, and split.Comment: 11 pages, 9 figures, 4 lemmas, 1 theorem, preprint of Workshop on
Computation: Theory and Practice 2012 at DLSU, Manila together with UP
Diliman, DLSU, Tokyo Institute of Technology, and Osaka universit
Computing with cells: membrane systems - some complexity issues.
Membrane computing is a branch of natural computing which abstracts computing models from the structure and the functioning of the living cell. The main ingredients of membrane systems, called P systems, are (i) the membrane structure, which consists of a hierarchical arrangements of membranes which delimit compartments where (ii) multisets of symbols, called objects, evolve according to (iii) sets of rules which are localised and associated with compartments. By using the rules in a nondeterministic/deterministic maximally parallel manner, transitions between the system configurations can be obtained. A sequence of transitions is a computation of how the system is evolving. Various ways of controlling the transfer of objects from one membrane to another and applying the rules, as well as possibilities to dissolve, divide or create membranes have been studied. Membrane systems have a great potential for implementing massively concurrent systems in an efficient way that would allow us to solve currently intractable problems once future biotechnology gives way to a practical bio-realization. In this paper we survey some interesting and fundamental complexity issues such as universality vs. nonuniversality, determinism vs. nondeterminism, membrane and alphabet size hierarchies, characterizations of context-sensitive languages and other language classes and various notions of parallelism
Bounded Languages Meet Cellular Automata with Sparse Communication
Cellular automata are one-dimensional arrays of interconnected interacting
finite automata. We investigate one of the weakest classes, the real-time
one-way cellular automata, and impose an additional restriction on their
inter-cell communication by bounding the number of allowed uses of the links
between cells. Moreover, we consider the devices as acceptors for bounded
languages in order to explore the borderline at which non-trivial decidability
problems of cellular automata classes become decidable. It is shown that even
devices with drastically reduced communication, that is, each two neighboring
cells may communicate only constantly often, accept bounded languages that are
not semilinear. If the number of communications is at least logarithmic in the
length of the input, several problems are undecidable. The same result is
obtained for classes where the total number of communications during a
computation is linearly bounded
On Languages Accepted by P/T Systems Composed of joins
Recently, some studies linked the computational power of abstract computing
systems based on multiset rewriting to models of Petri nets and the computation
power of these nets to their topology. In turn, the computational power of
these abstract computing devices can be understood by just looking at their
topology, that is, information flow.
Here we continue this line of research introducing J languages and proving
that they can be accepted by place/transition systems whose underlying net is
composed only of joins. Moreover, we investigate how J languages relate to
other families of formal languages. In particular, we show that every J
language can be accepted by a log n space-bounded non-deterministic Turing
machine with a one-way read-only input. We also show that every J language has
a semilinear Parikh map and that J languages and context-free languages (CFLs)
are incomparable
Asynchronous spiking neural P systems
We consider here spiking neural P systems with a non-synchronized (i.e., asynchronous) use of rules: in any step, a neuron can apply or not apply its rules which are enabled by the number of spikes it contains (further spikes can come, thus changing the rules enabled in the next step). Because the time between two firings of the output neuron is now irrelevant, the result of a computation is the number of spikes sent out by the system, not the distance between certain spikes leaving the system. The additional non-determinism introduced in the functioning of the system by the non-synchronization is proved not to decrease the computing power in the case of using extended rules (several spikes can be produced by a rule). That is, we obtain again the equivalence with Turing machines (interpreted as generators of sets of (vectors of) numbers). However, this problem remains open for the case of standard spiking neural P systems, whose rules can only produce one spike. On the other hand we prove that asynchronous systems, with extended rules, and where each neuron is either bounded or unbounded, are not computationally complete. For these systems, the configuration reachability, membership (in terms of generated vectors), emptiness, infiniteness, and disjointness problems are shown to be decidable. However, containment and equivalence are undecidable. © 2009 Elsevier B.V. All rights reserved
The Brightest Cluster Galaxy in Abell 85: The Largest Core Known so far
We have found that the brightest cluster galaxy (BCG) in Abell~85, Holm 15A,
displays the largest core so far known. Its cusp radius, kpc (), is more than 18 times
larger than the mean for BCGs, and kpc larger than A2261-BCG, hitherto
the largest-cored BCG (Postman, Lauer, Donahue, et al. 2012) Holm 15A hosts the
luminous amorphous radio source 0039-095B and has the optical signature of a
LINER. Scaling laws indicate that this core could host a supermassive black
hole (SMBH) of mass . We
suggest that cores this large represent a relatively short phase in the
evolution of BCGs, whereas the masses of their associated SBMH might be set by
initial conditions.Comment: 14 pages, 3 figure, 2 tables, accepted for publication in ApJ Letters
on October 6th, 2014, replacement of previous manuscript submitted on May
30th, 2014 to astro-p
Cosmic rays from Leptonic Dark Matter
If dark matter possesses a lepton number, it is natural to expect the
dark-matter annihilation and/or decay mainly produces the standard model
leptons, while negligible amount of the antiproton is produced. To illustrate
such a simple idea, we consider a scenario that a right-handed sneutrino dark
matter decays into the standard model particles through tiny R-parity violating
interactions. Interestingly enough, charged leptons as well as neutrinos are
directly produced, and they can lead to a sharp peak in the predicted positron
fraction. Moreover, the decay of the right-handed sneutrino also generates
diffuse continuum gamma rays which may account for the excess observed by
EGRET, while the primary antiproton flux can be suppressed. Those predictions
on the cosmic-ray fluxes of the positrons, gamma rays and antiprotons will be
tested by the PAMELA and FGST observatories.Comment: 21 pages, 4 figures, 2 tables, updated plots including PAMELA dat
On the Complexity of Searching in Trees: Average-case Minimization
We focus on the average-case analysis: A function w : V -> Z+ is given which
defines the likelihood for a node to be the one marked, and we want the
strategy that minimizes the expected number of queries. Prior to this paper,
very little was known about this natural question and the complexity of the
problem had remained so far an open question.
We close this question and prove that the above tree search problem is
NP-complete even for the class of trees with diameter at most 4. This results
in a complete characterization of the complexity of the problem with respect to
the diameter size. In fact, for diameter not larger than 3 the problem can be
shown to be polynomially solvable using a dynamic programming approach.
In addition we prove that the problem is NP-complete even for the class of
trees of maximum degree at most 16. To the best of our knowledge, the only
known result in this direction is that the tree search problem is solvable in
O(|V| log|V|) time for trees with degree at most 2 (paths).
We match the above complexity results with a tight algorithmic analysis. We
first show that a natural greedy algorithm attains a 2-approximation.
Furthermore, for the bounded degree instances, we show that any optimal
strategy (i.e., one that minimizes the expected number of queries) performs at
most O(\Delta(T) (log |V| + log w(T))) queries in the worst case, where w(T) is
the sum of the likelihoods of the nodes of T and \Delta(T) is the maximum
degree of T. We combine this result with a non-trivial exponential time
algorithm to provide an FPTAS for trees with bounded degree
The Mediterranean diet and micronutrient levels in depressive patients
Introduction: An inverse association between depression and some serum micronutrient levels (selenium, zinc, iron, magnesium, vitamin B and folic acid) has been reported. In addition, other studies reported that this micronutrient supplementation may improve depressed mood. The Mediterranean diet contains a sufficient amount of the micronutrients mentioned, although no study has reported an association between diet prescription and increased levels of them in depressive patients.
Objective: To examine the impact of dietary patterns recommendations on micronutrient levels in depressive patients.
Methods: 77 outpatients were randomly assigned either to the active (hygienic-dietary recommendations on diet, exercise, sleep, and sun exposure) or control group. Outcome measures were assessed before and after the six month intervention period.
Results: Serum selenium and zinc levels were slightly low at basal point and serum selenium was inversely correlated with severity of depression (r=-0.233; p=0.041). A better outcome of depressive symptoms was found in the active group. Nevertheless, no significant differences in micronutrient levels were observed after the Mediterranean diet pattern prescription, probably due to an insufficient adherence.
Conclusion: Selenium, zinc, iron, magnesium, vitamin B12 and folic acid serum levels didn`t increase in depressed patients after six months of the Mediterranean diet pattern prescription
Experimental study of MMI structures in a switchable continuous-wave thulium-doped all-fiber laser
Switchable multi-wavelength laser emission from a thulium-doped all-fiber laser is reported by implementing a tapered and a non-tapered multi-modal interference (MMI) filters. The MMI structure relies on a coreless optical fiber spliced in between two single-mode optical fibers. For the non-tapered case, a minimum insertion loss of 12.60 dB is achieved around the 2-μm region, from which stable generation of commutable dual-wavelength emission at 1986.34 nm and 2017.38 nm is obtained. On the other hand, the tapered MMI structure performs a minimum insertion loss of 8.74 dB at the 2-μm region, allowing a stable triple-wavelength emission at 1995.4 nm, 2013.3 nm, and 2038.3 nm. In addition, commutable dual-wavelength emission was also obtained at 1997.9 nm and 2032.1 nm. The generated laser lines perform bandwidths of around 50 pm, low peak spectral power fluctuations and signal-to-noise ratio of 50 dB
- …