Universal Machine Research Articles

MineCam: Application of Combined Remote Sensing and Machine Learning for Segmentation and Change Detection of Mining Areas Enabling Multi-Purpose Monitoring

Our study addresses the need for universal monitoring solutions given the diverse environmental impacts of surface mining operations. We present a solution combining remote sensing and machine learning techniques, utilizing a dataset of over 2000 satellite images annotated with ten distinct labels indicating mining area components. We tested various approaches to develop comprehensive yet universal machine learning models for mining area segmentation. This involved considering different types of mines, raw materials, and geographical locations. We evaluated multiple satellite data set combinations to determine optimal outcomes. The results suggest that radar and multispectral data fusion did not significantly improve the models’ performance, and the addition of further channels led to the degradation of the metrics. Despite variations in mine type or extracted material, the models’ effectiveness remained within an Intersection over Union value range of 0.65–0.75. Further, in this research, we conducted a detailed visual analysis of the models’ outcomes to identify areas requiring additional attention, contributing to the discourse on effective mining area monitoring and management methodologies. The visual examination of models’ outputs provides insights for future model enhancement and highlights unique segmentation challenges within mining areas.

Lower bounds on β ( α ) and other properties of α-register machines

This paper extends our paper (In Revolutions and Revelations in Computability. CiE 2022 (2022)) for the conference “Computability in Europe” 2022. After Infinite Time Turing Machines (ITTM) were introduced in Hamkins and Lewis (Journal of Symbolic Logic 65 (2000)), a number of machine models of computability have been generalized to the transfinite. While for some of these models the computational strength has been successfully determined, there are still several white spots on the map of transfinite computability. In this paper, we contribute to the understanding of the computational strength of transfinite machine models by (i) proving lower bounds on the computational strength of α-Infinite Time Register Machines (α-ITRMs) for certain values of α, refuting a conjecture about their strength made in (Annals of Pure and Applied Logic 173 (2022)), (ii) showing that the computational strength of cardinal-recognizing ITRMs is equal to that of ITRMs and (iii) showing that non-solvability of the bounded halting problem, existence of a universal machine and an increase of computational power by allowing machines to recognize cardinals are equivalent for α-ITRMs for all relevant values of α. Finally, we give some results indicating how the picture changes when the use of parameters is dropped or restricted.

Emergent Information Processing: Observations, Experiments, and Future Directions

Science is currently becoming aware of the challenges in the understanding of the very root mechanisms of massively parallel computations that are observed in literally all scientific disciplines, ranging from cosmology to physics, chemistry, biochemistry, and biology. This leads us to the main motivation and simultaneously to the central thesis of this review: “Can we design artificial, massively parallel, self-organized, emergent, error-resilient computational environments?” The thesis is solely studied on cellular automata. Initially, an overview of the basic building blocks enabling us to reach this end goal is provided. Important information dealing with this topic is reviewed along with highly expressive animations generated by the open-source, Python, cellular automata software GoL-N24. A large number of simulations along with examples and counter-examples, finalized by a list of the future directions, are giving hints and partial answers to the main thesis. Together, these pose the crucial question of whether there is something deeper beyond the Turing machine theoretical description of massively parallel computing. The perspective, future directions, including applications in robotics and biology of this research, are discussed in the light of known information.

People and machines in communication / Personas y máquinas en comunicación

It was 1937 when Alan Turing published his most famous article in the Proceedings of the London Mathematical Society. In this work, for the first time, he presented an idealized description of the mathematical inner workings of such universal machines as would eventually become instantiated in what we now call computers. This extraordinary step in the history of ideas provided a theoretical boon that later on would prove important for the development of the computational theory of mind. According to this theory, the cognitive processes of human beings could be likened to the algorithms that apply to the representations of the external world. Based on this hypothesis, since the middle of the last century, attempts have been made to replicate the functioning of the human mind using a computer. The aim of this article is to present the differences that still exist between humans and intelligent machines. From ELIZA onwards, we have seen several developments including ALICE, up to XiaoIce. Despite the evolution of intelligent machines and the creation of social chatbots in particular, artificial intelligence still has shortcomings that set it apart from man: the way it knows, the lack of consciousness and of agency.

Comparative evaluation of two cetylpyridinium chloride-based mouthwashes on the mechanical properties and strength loss of elastomeric chains used in dentistry: An vitro study

ObjectivesEvaluate the strength degradation of polymeric ligature chains after their immersion in cetylpyridinium chloride-based mouthwashes. Methods240 elastomeric samples from four different manufacturers (Rocky Mountain®, Ormco®, Morelli® and Dentaurum®) in two types of configurations (with and without intermodular links) and divided in 3 groups (distilled water, Vitis CPC Protect® and PERIO·AID® 0.05%) at 5 follow-up periods (0–24 h, 7–14 -21 days) were immersed twice a day for 60 s, following the manufacturers' protocols. A universal traction machine was used to perform the measurements and a post hoc multiple comparisons were based on the Bonferroni test and extended to a 3-way ANOVA test (α = 0.05). ResultsThere was a drop in strength up to 35.9% at 24 h. After a week, the short chains (52%) degraded less than the long ones (57.3%) with significant differences (p < 0.001) and the same pattern was observed until 21 days (p < 0.001). At 24 h, the degradation of the chains exposed in distilled water was 25.8%, in VITIS CPC Protect® 28.6% and in PERIO· AID® 0.05%, 27% with significant differences (p < 0.001). At 21 days, the VITIS CPC Protect® group obtained a much greater loss of strength, being this drop statistically significant (p < 0.001). The chains from Ormco® and RMO® experienced the least loss of force when immersed in the control group or PERIO AID® 0 0.05% (48% and 51%), while Dentaurum's in VITIS CPC Protect® lost more than 75%. ConclusionsThe orthodontic elastomeric chains suffer a sharp drop in strength during the first days of treatment. When comparing the mouthwashes, there were statistically significant differences in terms of strength degradation. Clinical significanceBased on the results, some types of chains, such as the ones without intermodular links from Ormco® showed better properties throughout the study. When immersed in PERIO·AID®0.05%, all showed significantly better results over time. Thus, PERIO·AID®0.05% can be recommended as a complementary oral hygiene element in dental treatments when elastomeric chains are used.

PROBLEMS OF CONSTRUCTION AND OPERATION OF BUILDINGS AND STRUCTURES IN THE CONDITIONS OF RECONSTRUCTION AND RESTORATION USING UNIVERSAL MACHINES

The article considers modern landscape and development vectors in the field of reconstruction and restoration where universal machines are applied. As practical examples, two options are considered: the technology of superstructure of the attic floor superstructure with enlarged metal block sections and superstructure of the attic floor from lightweight aerated concrete blocks. The possibilities of using BIM and robotics in reconstruction and restoration are analyzed.

STUDY OF LUBRICANT ADDITIVES FOR EXPANSION PIPE EXPANSION IN MONODIAMETER WELLS

There is a need to improve well design and completion in order to reduce material intensity while maintaining sufficient casing cross-sections. One of the possible solutions for this is the construction of mono-diameter wells using expandable casing technology. The technology of drilling wells with the same fixed bore diameter from the wellhead to the productive formation could solve many problems and limitations in the construction of wells, opening up opportunities for the development of large oil and gas reserves that are currently classified as difficult to recover or inaccessible. The technology of drilling monodiameter wells also reduces drilling volumes, reduces the adverse impact on the environment and, ultimately, leads to minimization of construction costs.For purposeful choice of flushing fluid components, especially reagents of complex action and lubricating additives necessary for drilling of mono-diameter wells, their preliminary laboratory tests on experimental installations providing physical similarity of interaction processes (wear) of friction pairs in relation to drilling technology are required. The task of this article is to study lubricating additives for reaming of reaming pipe in mono-diameter wells for subsequent selection of the most optimal of them. The experiments were carried out on the wellknown universal machine II 5018, designed for testing friction and wear of metals and alloys, hard engineering plastics and composites. The loading system and the II 5018 work unit were upgraded to simulate the processes being studied. During the experiments, the friction coefficient and wear rate of the sample were measured. To carry out the research, various lubricating and cooling media used in drilling technology were selected.

Comparative Evaluation of Push-out Bond Strength of Three Different Root Canal Sealers: An In Vitro Study.

The aim of this present study was to compare the dislodgement resistance of calcium silicate-based sealer, zinc oxide sealer, and a new sealer combining both zinc oxide and calcium silicate-based sealer in vitro. 60 single-rooted human teeth were instrumented with F3 Protaper Gold. All endodontic canals were filled using gutta percha cones using the cold lateral condensation technique in combination using one of the mentioned sealers (n = 20 per group). The teeth were divided into three groups: group A consisted of Sealite® Ultra, group B consisted of K-Sealer®, and group C consisted of BioRoot® RC. After 2 months of incubation (37°C, 100% humidity) and after cutting out 2 mm from the most apical portion of the root apex, six slices of 1 mm thickness were generated. Mechanical dislodgement resistance was examined using a universal pressure-testing machine and the push-out bond strength (POBS) was calculated. Specimens were examined under 20× magnification to define the bond failure mode. Statistical analysis was executed using ANOVA, post hoc Turkey test for pairwise comparisons and Kruskal-Wallis tests. The POBS of BioRoot® was significantly higher than the POBS of the two other sealers with a mean of 10.54 MPa ± 2.10 and 5.73 MPa ± 2.34, respectively (p < 0.001). Sealite® and K-Sealer® showed similar results in the median and coronal part. K-Sealer® revealed highest POBS compared with Sealite® in the apical part (p < 0.05). The POBS of the zinc oxide and calcium silicate-based sealer was significantly lower compared with calcium silicate. Sealite® and K-Sealer® exhibited almost same results. BioRoot showed the highest POBS of all sealers. The current study was needed to evaluate the bond strength of three different cements to dentinal walls, by evaluating their respective POBS in vitro. The findings of this study may provide guidance for the clinician in the selection of an adequate endodontic sealer that guarantees an enhanced adhesive seal between the Gutta-percha and the dentinal canal walls. How to cite this article: Makhlouf MP, El Helou JD, Zogheib CE, et al. Comparative Evaluation of Push-out Bond Strength of Three Different Root Canal Sealers: An In Vitro Study. J Contemp Dent Pract 2024;25(1):15-19.

Correlating Frictional Forces Generated by Different Bracket Types during Sliding and Surface Topography Using Scanning Electron Microscopy and Optical Profilometer.

The study aims to correlate the frictional forces (FF) of four different types of commercially available ceramic brackets to their surface topography. Two monocrystalline (MC) brackets (CLEAR™, Adanta, Germany; Inspire ICE™, Ormco, USA), one polycrystalline (PC) bracket (Symetri Clear™, Ormco, USA), one clear hybrid esthetic bracket (DISCREET™, Adanta, Germany), and a stainless-steel (SS) bracket (Victory™, 3M Unitek, USA) served as control. Both static friction (SF) and kinetic friction (KF) were recorded during sliding using an Instron universal machine in dry settings. The bracket slot surface topography was evaluated. A scanning electron microscope (SEM) and a profilometer machine were used for assessment before and after sliding. Frictional forces values during sliding were as follows in descending order; Inspire ICE™, CLEAR™, DISCREET™, Symetri Clear™, and, lastly, Victory™. Also, DISCREET™ scored the highest in surface roughness (Sa) values followed by Symetri Clear™. None of the correlations were statistically significant. Frictional forces produced during sliding were not always directly related to surface roughness. Monocrystalline ceramic brackets appeared to have the greatest FF and a low surface roughness. Furthermore, DISCREET™ scored a very low frictional value comparable to metal brackets yet showed the highest surface roughness. Metal brackets exhibited the greatest surface smoothness before sliding and the least SF. Predicting the FFs produced during sliding mechanics would help the practitioner while choosing the bracket system to be used, and while planning the treatment mechanics, how much force to deliver, and how much tooth movement to expect. How to cite this article: AlBadr AH, Talic NF. Correlating Frictional Forces Generated by Different Bracket Types during Sliding and Surface Topography Using Scanning Electron Microscopy and Optical Profilometer. J Contemp Dent Pract 2024;25(1):41-51.

Constructive Separations and Their Consequences

For a complexity class $C$ and language $L$, a constructive separation of $L \notin C$ gives an efficient algorithm (also called a refuter) to find counterexamples (bad inputs) for every $C$-algorithm attempting to decide $L$. We study the questions: Which lower bounds can be made constructive? What are the consequences of constructive separations? We build a case that "constructiveness" serves as a dividing line between many weak lower bounds we know how to prove, and strong lower bounds against $P$, $ZPP$, and $BPP$. Put another way, constructiveness is the opposite of a complexity barrier: it is a property we want lower bounds to have. Our results fall into three broad categories. 1. Our first set of results shows that, for many well-known lower bounds against streaming algorithms, one-tape Turing machines, and query complexity, as well as lower bounds for the Minimum Circuit Size Problem, making these lower bounds constructive would imply breakthrough separations ranging from $EXP \neq BPP$ to even $P \neq NP$. 2. Our second set of results shows that for most major open problems in lower bounds against $P$, $ZPP$, and $BPP$, including $P \neq NP$, $P \neq PSPACE$, $P \neq PP$, $ZPP \neq EXP$, and $BPP \neq NEXP$, any proof of the separation would further imply a constructive separation. Our results generalize earlier results for $P \neq NP$ [Gutfreund, Shaltiel, and Ta-Shma, CCC 2005] and $BPP \neq NEXP$ [Dolev, Fandina and Gutfreund, CIAC 2013]. 3. Our third set of results shows that certain complexity separations cannot be made constructive. We observe that for all super-polynomially growing functions $t$, there are no constructive separations for detecting high $t$-time Kolmogorov complexity (a task which is known to be not in $P$) from any complexity class, unconditionally.

Life as the Explanation of the Measurement Problem

This study argues that a biological cell, a dissipative structure, is the smallest agent capable of processing quantum information through its triangulated, holographic sphere of perception, where this mechanism has been extended by natural evolution to endo and exosemiosis in multicellular organisms and further to the language of Homo sapiens. Thus, life explains the measurement problem of quantum theory within the framework of the holographic principle, emergent gravity, and emergent dimensionality. Each Planck triangle on a black hole surface corresponds to a qubit in an equal superposition, attaining known bounds on the products of its energies and orthogonalization interval. Black holes generate entropy variation shells through the solid-angle correspondence. The entropic work introduces the bounds on the number of active Planck triangles dependent on the information capacity of the black hole generator. The velocity and dissipativity bounds and the bounds on the theoretical probabilities for active, energy-carrying Planck triangles were derived. In particular, this study shows that black holes, Turing machines, and viruses cannot assume the role of an observer. The entropy variation shells and black-body objects may hint at solutions to ball lightning and sonoluminescence unexplained physical spherical phenomena.“It is also possible that we learned that the principal problem is no longer the fight with the adversities of nature but the difficulty of understanding ourselves if we want to survive” [1].

Turing Machine Halting Problem, Russell’s Paradox and Gödel Incompleteness Theorem

The Turing Machine Halting Problem is a major problem in computer theory, Russell’s Paradox is the root of the Third Mathematical Crisis, and the Gödel Incompleteness Theorem is a major discovery in modern logic. The three have had a profound impact on the development of science and have attracted the attention of scientific and philosophical circles. However, since the Gödel Incompleteness Theorem was put forward, the scientific and philosophical significance of its proof has been questioned; in particular, Wittgenstein regards it as a certain logical paradox, and Russell’s Paradox has not yet been settled. This paper makes a detailed analysis of the three based on the view of dialectical infinity. The author notes that the Principle of Comprehension based on the view of actual infinity is the root of Russell’s Paradox. The Turing Machine Halting Problem shows that it is impossible to make an actual-infinite ultimate judgment of the constantly generated infinite world, but the philosophical significance of the Gödel Incompleteness Theorem is that our understanding of the world is essentially potentially infinite. At the end of the article, the author raises several questions about the proof of the Gödel Incompleteness Theorem, finds out the specific paradox form in the proof, points out the high consistency of its proof method and Russell’s Paradox, which strongly supports Wittgenstein’s view. The author points out that the philosophical basis of the proof of the Gödel Incompleteness Theorem is the idea of actual infinity, the proof of the theorem is based on a logically invalid circular formula, the contradiction of the proof originates from the Gödel formula itself, and cannot be attributed to the incompleteness of the system, so the proof is wrong. Therefore, the conclusion of this paper is that the world is constantly developing and changing, and our human understanding of the world is essentially a potential infinite, that is, the world is Aristotelian, not Platonic.

Microstructure and Mechanical Characterization of Rice Husks from the Tolima Region of Colombia

The under-utilization of rice husk, a milling by-product, demands attention due to its widespread disposal and limited usage. This research aims to assess the physical properties and mechanical behavior of three rice husk varieties (F 2000, Orizyca, and Panorama 394), to determine their strength capacities and potential applications. Mechanical properties are evaluated through a non-standardized tension test using a universal machine. Subsequent analyses include measuring the moisture content following ASTM D1348, determining the particle size distribution through ASAE Standard S319, and establishing the bulk density using ASAE Standard S269 Method 4. Mechanical resistance in the rice husk varieties ranged from 60 MPa to 130 MPa, with a particle density exceeding 300 kg/m3 and an average apparent density of 140 kg/m3. Scanning electron microscopy revealed the husk structures, identifying epidermis, hypodermis, and sub-hypodermis layers. The mechanical stress of the Orizyca variety was 1.89 times higher than that of F 2000, and 1.18 times higher than that of Panorama 394. Potential applications include brick manufacturing and thermoformed materials for Orizyca and Panorama 394, while F 2000 could be utilized for producing fuel briquettes or cardboard, among other possibilities.

Exploring Quantum Computing Paradigm: From Conceptualisation, Initial Adoption to Development

Quantum computing (QC) holds promise for next-generation applications that requires exponential time to solve NP problems. However, even after 25+ years, researchers still struggle with stable error correction solutions for delivering a stable commercialised quantum universal quantum machine. Companies like IBM, Rigetti, and D-Wave have already started offering quantum annealers, intermediate quantum devices based on the qubit. Therefore, researchers believe that QC would be introduced as an extension of classical computers (CC), where CC would offload a specific computational intensive task. Cloud companies, including Amazon, Azure, and IBM, have already begun to provide cloud services where an organisation can use a QC to work on potential applications. This paper systematically analyses the need to provide QC as a service (QCaaS) for potential applications. Furthermore, we discuss the framework on which this service can be offered. Subsequently, we provide a detailed discussion of various toolkits, libraries, and simulators available for QC.

Emergence of Universal Computations Through Neural Manifold Dynamics.

There is growing evidence that many forms of neural computation may be implemented by low-dimensional dynamics unfolding at the population scale. However, neither the connectivity structure nor the general capabilities of these embedded dynamical processes are currently understood. In this work, the two most common formalisms of firing-rate models are evaluated using tools from analysis, topology, and nonlinear dynamics in order to provide plausible explanations for these problems. It is shown that low-rank structured connectivities predict the formation of invariant and globally attracting manifolds in all these models. Regarding the dynamics arising in these manifolds, it is proved they are topologically equivalent across the considered formalisms. This letter also shows that under the low-rank hypothesis, the flows emerging in neural manifolds, including input-driven systems, are universal, which broadens previous findings. It explores how low-dimensional orbits can bear the production of continuous sets of muscular trajectories, the implementation of central pattern generators, and the storage of memory states. These dynamics can robustly simulate any Turing machine over arbitrary bounded memory strings, virtually endowing rate models with the power of universal computation. In addition, the letter shows how the low-rank hypothesis predicts the parsimonious correlation structure observed in cortical activity. Finally, it discusses how this theory could provide a useful tool from which to study neuropsychological phenomena using mathematical methods.

Quantum Kolmogorov complexity and quantum correlations in deterministic-control quantum Turing machines

This work presents a study of Kolmogorov complexity for general quantum states from the perspective of deterministic-control quantum Turing Machines (dcq-TM). We extend the dcq-TM model to incorporate mixed state inputs and outputs, and define dcq-computable states as those that can be approximated by a dcq-TM. Moreover, we introduce (conditional) Kolmogorov complexity of quantum states and use it to study three particular aspects of the algorithmic information contained in a quantum state: a comparison of the information in a quantum state with that of its classical representation as an array of real numbers, an exploration of the limits of quantum state copying in the context of algorithmic complexity, and study of the complexity of correlations in quantum systems, resulting in a correlation-aware definition for algorithmic mutual information that satisfies symmetry of information property.

Ensuring quick changeability of the working bodies of technological machines in the construction and maintenance of the landscape, road-building, and agricultural industries

The relevance of the subject matter is conditioned by the high-efficiency use of reconfigurable manufacturing systems during construction work and the associated need to develop and implement technological machines with replaceable working bodies. The purpose of this study is to analyze the invariance of the equipment used by types of work in landscape and landscape construction. The study used theoretical methods of analysis and synthesis of information on the principles of the practical application of a universal machine with a wide range of mounted technological working bodies. The results obtained indicate the high relevance of the issue of the rapid changeability of mounted technological working bodies. Its effective solution lies in the creation of reconfigurable production machines based on a universal wheelbase with replaceable working bodies of variable layout by type of work, for which a new design of an inter-module basing and fastening device is proposed. The possibility of its practical application in the BobCat loader system is considered. It is established that, in general, the use of the BobTach mounting frame during various technological operations ensures an increase in the efficiency of this technological equipment. In addition, it significantly increases the performance of the entire model range of equipment and testifies to the versatility of the specified mounting frame. The practical significance of the results obtained is conditioned by the possibility of their application in the development and implementation of modern technological machines with rapidly replaceable working bodies in the agricultural sector and road construction.

Cognitive paradoxes and brain mechanisms

It is generally agreed amongst philosophers and neuroscientists that the main obstacle between the science of the brain and the conscious nature of the mind is rooted in an objective-subjective dichotomy. It is further common to classify natural sciences in terms of their epistemological values and their ontological existential attributes. As a result, one concludes that a computer that is useful for studying nature, such as the conscious mind, is not itself part of nature, or as phrased differently by the noted philosopher, John Searle, ‘there are no Turing Machines in nature! However, the great physicist John Archibald Wheeler, by declaring the famous dictum, ‘it from bit’, did impart a somewhat different approach to the true nature of reality. To reconcile the two contrasting portraits, a different picture, based on the principle of self-reference, will be presented, and applied to the brain-mind problem. It is demonstrated how this principle imparts a thermo-qubit syntax, i.e., ‘bit from it’, for communication between increasingly more complex physical systems. Altogether, the steady state situation produces negentropic pockets for quantification and storage of information. The communication protocol entails cognition mechanisms that display unexpected equivalences that prompts fundamental interpretations of general optical illusions such as Necker’s cube, the Rubin vase, and the Spinning Dancer. The derived syntax also embodies an interesting deconstruction of the recently observed dodecanogram brain signal, experimentally elucidated by Anirban Bandyopadhyay and his team.

The mode of computing

The Turing Machine is the paradigmatic case of computing machines, but there are others such as analogical, connectionist, quantum and diverse forms of unconventional computing, each based on a particular intuition of the phenomenon of computing. This variety can be captured in terms of system levels, re-interpreting and generalizing Newell’s hierarchy, which includes the knowledge level at the top and the symbol level immediately below it. In this re-interpretation the knowledge level consists of human knowledge and the symbol level is generalized into a new level that here is called The Mode of Computing. Mental processes performed by natural brains are often thought of informally as computing processes and that the brain is alike to computing machinery. However, if natural computing does exist it should be characterized on its own. A proposal to such an effect is that natural computing appeared when interpretations were first made by biological entities, so natural computing and interpreting are two aspects of the same phenomenon, or that consciousness and experience are the manifestations of computing/interpreting. By analogy with computing machinery, there must be a system level at the top of the neural circuitry and directly below the knowledge level that is named here The mode of Natural Computing. If it turns out that such putative object does not exist the proposition that the mind is a computing process should be dropped; but characterizing it would come with solving the hard problem of consciousness.

Universal machine learning aided synthesis approach of two-dimensional perovskites in a typical laboratory

The past decade has witnessed the significant efforts in novel material discovery in the use of data-driven techniques, in particular, machine learning (ML). However, since it needs to consider the precursors, experimental conditions, and availability of reactants, material synthesis is generally much more complex than property and structure prediction, and very few computational predictions are experimentally realized. To solve these challenges, a universal framework that integrates high-throughput experiments, a priori knowledge of chemistry, and ML techniques such as subgroup discovery and support vector machine is proposed to guide the experimental synthesis of materials, which is capable of disclosing structure-property relationship hidden in high-throughput experiments and rapidly screening out materials with high synthesis feasibility from vast chemical space. Through application of our approach to challenging and consequential synthesis problem of 2D silver/bismuth organic-inorganic hybrid perovskites, we have increased the success rate of the synthesis feasibility by a factor of four relative to traditional approaches. This study provides a practical route for solving multidimensional chemical acceleration problems with small dataset from typical laboratory with limited experimental resources available.