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The study of alternation in two-way finite automata ( 2 fa s) has been quite non-systematic. Since the 1970's, various authors with a variety of motivations have studied 2 fa s with various types of alternation and a variety of names, creating a fairly long list of sporadic contributions with little internal consistency. This article attempts to organize the subject into a single unifying framework. We start with a detailed account of all contributions to date, that reveals the large variety of approaches and the lack of consistency between them. We then identify and name four types of automata that these contributions have really studied over the years: general two-way Boolean finite automata ( 2 b fa s); monotone 2 b fa s; basic 2 b fa s; and (monotone basic, or) alternating 2 b fa s ( 2 a fa s). Next, we identify four different ways by which authors have described how such automata compute, each offering a distinct view onto their operation: the circuit view, where computation is modelled by a circuit of Boolean gates; the formula view, where computation is modelled by a Boolean formula over configuration-variables; the run view, where decisions are determined by the existence of appropriate trees of configuration-goal pairs, called “runs”; and the (most classic) tree view, where computation is modelled by a tree of configurations. After carefully defining each 2 b fa type and each view, we prove the following. First, that within each type, every two of the four views are equivalent to each other, in the strong sense that each of them closely mimics the other at every step of the computation. Second, that not all types of 2 b fa s are equivalent: although general 2 b fa s are as powerful as monotone 2 b fa s, and basic 2 b fa s are as powerful as 2 a fa s (up to polynomial differences in the number of states), general 2 b fa s may need exponentially fewer states than 2 a fa s.

This article investigates the problem of deploying a swarm of UAVs equipped with gas sensors for industrial remote gas-plume sensing. This setup’s objective is to continuously adjust the swarm formation to maximize the combined perception for the dynamically evolved plume’s cloud, focusing around areas with the highest concentration/intensity. Initially, such a setup is formulated into an optimization problem, the solution of which could be acquired by the maximization of an appropriately defined objective function. Due to the model-free approach, this objective function’s analytical form is not available, prohibiting standard gradient descent methodologies. To this end, a tracking algorithm is developed and studied, which operates in a distributed manner and enables the UAV swarm to build a common consensus dynamically, during the evolution of the leakage phenomenon. The overall performance is tested in a simulative yet realistic environment using ANSYS Fluent suite, considering a simultaneous gas-leak incident at two different points. Aside from the standalone evaluation study, the proposed gas-plume tracking scheme is able to outperform a state-of-the-art alternative algorithm, namely Efficient Global Optimization (EGO), in various simulation setups, deploying a different number of UAVs on the field.

Within the project NOPTILUS, a fully functional system/methodology had been developed that allows the cooperative, fully-autonomous navigation of teams of AUVs when deployed in Static or Dynamic Underwater Map Construction (SDUMC) or Dynamic Underwater Phenomena Tracking (DUPT) missions. The key ingredient of this fully functional system/methodology (called the NOPTILUS Planning, Assignment and Navigation Module - NOPTILUS PAN) is an optimal control algorithm - called Parametrized Cognitive Adaptive Optmization - (PCAO) - developed by one of the NOPTILUS partners (CERTH). PCAO is firstly tailored and modified so as to be applicable to the problem of autonomous navigation of teams of AUVs when deployed in SDUMC or DUPT missions. For this purpose, a nonlinear model is developed so as to capture the dynamics of the AUVs, their sensors and the underwater environment. More precisely, the original PCAO-based approach is revised so as to be able to efficiently handle information coming from the localization module, the underwater acoustic communication module, the situation understanding module as well as instructions from the operator. The information coming from these modules is handled by the NOPTILUS PAN module without the need to enter in tedious re-design tasks. Two real-life experiments (involving teams of AUVs deployed in static mapping or simultaneous static mapping and dynamic target taking) demonstrate the efficiency and practicability of the NOPTILUS PAN module.

On every n-long input, every two-way finite automaton (2fa) can reverse its input head O(n) times before halting. A 2fawith few reversals is an automaton where this number is only o(n). For every h, we exhibit a language that can be recognized by an h-state nondeterministic 2fa with few reversals, but requires @W(2^h) states on every deterministic 2fa with few reversals.

Osteoarthritis of the first carpometacarpal joint is the second most common site of osteoarthritis in humans. Symptomatic isolated scaphotrapeziotrapezoid joint arthritis, though less common overall, is also frequently observed by the hand surgeon. Investigations on the etiology, pathophysiology, natural history, outcomes of traditional treatments, and new forms of surgical techniques have been attracting more interest in the field of hand surgery. The goal of this article is to sort through the current prevailing ideas using recently available literature and to offer a concise, updated guide to further enhance the understanding of thumb carpometacarpal and scaphotrapeziotrapezoid arthritis.

We developed a two-study, cross-national, constructive replication to examine the role of organizational politics perceptions as a contextual moderator of the political skill – job performance relationship. Specifically, we hypothesized that high levels of political skill would demonstrate its strongest positive effects on job performance when politics perceptions were perceived as low. Conversely, we hypothesized that political skill would demonstrate no relationship with job performance under conditions of high politics perceptions. Across studies conducted both in the United States and Greece, the hypothesis received strong support. In settings characterized by lower perceived politics, high levels of political skill predicted significant increases in job performance, whereas these effects were attenuated in environments characterized by high perceived politics. Contributions and implications of this research, strengths and limitations, and directions for future study are discussed.

Background context Primary epitheliod hemangioendotheliomas of the lumbar spine are extremely rare tumors with an unpredictable clinical course. Purpose To present a case of primary lumbar epithelioid hemangioendothelioma and its treatment protocol. Study design/setting A tertiary Spinal Unit. Patient sample A previously healthy adult with persisting low back pain and neurologic deficit. Methods The diagnosis was confirmed by core needle biopsy. The patient was treated with preoperative embolization followed by staged surgery which included wide tumor resection and spinal fixation, using a cage system and a titanium plate anteriorly and a transpedicular fixation system posteriorly. Results Three years postoperatively the patient remains free of symptoms with no evidence of recurrence. Conclusions The treatment of these unpredictable tumors should be dictated by adherence to general oncologic principles.

It was demonstrated for a lithium silicate glass that the low temperature ( 200 K)–high frequency (GHz) conductivity have the same origin. Presumably, either when the temperature is too low or the time scale is too short to observe a single ion hopping, conductivity arises from the localized motion of a group of atoms like the ‘wiggling of a jellyfish’. Mathematically, this complex motion has been described at low temperatures in terms of the thermally activated motion of atoms over a distribution of asymmetric double well potential (ADWP). Empirical analysis of experimental data reveals that microwave conductivity, σMW, cannot be explained simply by the combined contribution of low frequency single ion hopping and far infrared (FIR) single ion vibrations. Computer simulations using the ADWP model explain the linear frequency dependence of microwave conductivity reasonably well and predict a plateau at high frequencies. Finally, the results of simulations are compared with the data to establish the relative contributions from ADWP excitations and from single ion vibrations to the experimentally observed conductivity at 108–1012 Hz frequency range.

Lithium metaborate-metaaluminate glasses x LiAlO 2 ·(1− x )LiBO 2 , (0≤ x ≤0.42), and crystals (Li 3 B 2 AlO 6 , Li 2 BAlO 4 ) have been prepared and studied by infrared and Raman spectroscopies. The two crystalline compounds have similar networks made of AlO 4 − and BO 2 O − units (O, O: bridging and terminal oxygen atoms, respectively) in arrangements which maximize the number of BOAl linkages. Both compounds decompose at high temperatures into α-LiBO 2 and γ-LiAlO 2 . Increasing x in glass induces the isomerization of BO 4 − tetrahedra to BO 2 O − triangles, while aluminum forms AlO 4 − units. This structural scheme is sufficient to account for the minimum in the glass transition temperature observed for x ≈ 0.25. There is no vibrational evidence for the presence of AlO 5 or AlO 6 polyhedra in glass, although their presence in small amounts cannot be excluded. Glasses and crystals of the same stoichiometry ( x = 0.33) are differentiated by an excess of kinetically arrested BOB and AlOAl linkages in the former.

RBa2Cu3O7 and [R0.5Pr0.5]Ba2Cu3O7 compounds with RY and lanthanides have been prepared and studied at ambient temperature by means of XRD and infrared-reflectance spectroscopy. In Pr free compounds, increasing the Shannon radius of R, rR, leaves the puckering of the Cu(2)−O(2, 3) sheet unaffected. In the Pr containing compounds, the PrO coordination polyhedron is typical of R+3 ions in eight-fold coordination and argues against differentiating Pr in terms of valence or hybridization. Instead, a repositioning of Ba within the cuprate block is observed, leading to the flattening of the sheet and the anomalously high frequency of the Ba and Cu(2)−O(2, 3) B1u modes. In RPr compounds the c-axis and the interplanar distances related to the position of Ba and O(2, 3) are found to exhibit a sigmoidal dependence on rR. It is argued that this sigmoidal dependence is related to the two-mode behavior exhibited by several phonon modes of these compounds.

The structure of glasses in the system Na 2 O · x R 2 O 3 · (3 − 2 x )SiO 2 (RAl, B) has been studied by employing Raman and infrared reflectance spectroscopies. These particular glass compositions were chosen for elucidating the role of aluminum and boron substitution on glass structure and properties while keeping the Na/(Si + R) ratio fixed. In the presence of aluminum, the equilibrium 2Q 3 ⇔ Q 4 + Q 2 shifts to the left. The role of boron was found to be the opposite, since it induces the destruction of the Q 3 species and the creation of the highly charged Q 2 and Q 1 species, as well as the fully polymerized Q 4 silicate units. The combined far-infrared and XPS results on the same glasses suggest that the average charge density of sites populated by sodium ions is smaller in aluminosilicate than in borosilicate glasses.

Vibrational and devitrification techniques are employed to investigate the structure and glass-forming ability of x NaBO 2 · (1 − x )LiBO 2 glasses with 0 ⩽ x ⩽ 0.75. Alkali substitution is found to result in non-additive network changes due to the appearance of structures encountered in the newly discovered compound Li 3 NaB 4 O 8 ( x = 0.25). A decrease of T g with x is observed and attributed mainly to the partial suppression of the formation of tetrahedra-containing, β′- and γ-LiBO 2 -type, arrangements in the glass network. The dependence of the crystallization products on temperature is very pronounced for x = 0 and progressively diminishes for x → 0.25. This diminishment is taken to indicate that, upon increasing x (0 ⩽ x ⩽ 0.25), the structural rearrangements associated with the liquid-to-glass transition become less pronounced. In turn, alkali mixing in the system under investigation is correlated with decreasing melt ‘fragility’ and a less pronounced pathway glass morphology. Such remarks may be important in assessing the mixed alkali effect from a structural viewpoint, especially since they are compatible with earlier findings on lower modification borate analogs.

The Raman spectra of crystals built solely of metaborate triangles provide fingerprint identification of three distinct network types. Classified according to increasing cation field strength these are: rings with degenerate intra-annular bonds and D 3 h symmetry, distorted rings with alternating intra-annular bonds and C 3 h symmetry, as well as chains. The occurrence of each network type has been associated with a characteristic range of cationic field strength. This approach led to the discovery of a hitherto unknown C 3 h ring strontium metaborate crystal, with Sr 2+ cations in 9- or 10-fold coordination to oxygen atoms. The Raman spectra of the mixed cation metaborates Ba 2 Ca(B 2 O 4 ) 3 and Ba 2 Mg(B 2 O 4 ) 3 confirm their C 3 h -ring structure and clearly point to the fact that the synergetic effect of dissimilar cations to the metaborate network cannot be predicted by the additivity of their field strengths.