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PubMed2004

Cognitive navigation based on nonuniform Gabor space sampling, unsupervised growing networks, and reinforcement learning.

We study spatial learning and navigation for autonomous agents. A state space representation is constructed by unsupervised Hebbian learning during exploration. As a result of learning, a representation of the continuous two-dimensional (2-D) manifold in the high-dimensional input space is found. The representation consists of a population of localized overlapping place fields covering the 2-D space densely and uniformly. This space coding is comparable to the representation provided by hippocampal place cells in rats. Place fields are learned by extracting spatio-temporal properties of the environment from sensory inputs. The visual scene is modeled using the responses of modified Gabor filters placed at the nodes of a sparse Log-polar graph. Visual sensory aliasing is eliminated by taking into account self-motion signals via path integration. This solves the hidden state problem and provides a suitable representation for applying reinforcement learning in continuous space for action selection. A temporal-difference prediction scheme is used to learn sensorimotor mappings to perform goal-oriented navigation. Population vector coding is employed to interpret ensemble neural activity. The model is validated on a mobile Khepera miniature robot.

Cognition↗
PubMed2004

Probabilistic space-time video modeling via piecewise GMM.

In this paper, we describe a statistical video representation and modeling scheme. Video representation schemes are needed to segment a video stream into meaningful video-objects, useful for later indexing and retrieval applications. In the proposed methodology, unsupervised clustering via Gaussian mixture modeling extracts coherent space-time regions in feature space, and corresponding coherent segments (video-regions) in the video content. A key feature of the system is the analysis of video input as a single entity as opposed to a sequence of separate frames. Space and time are treated uniformly. The probabilistic space-time video representation scheme is extended to a piecewise GMM framework in which a succession of GMMs are extracted for the video sequence, instead of a single global model for the entire sequence. The piecewise GMM framework allows for the analysis of extended video sequences and the description of nonlinear, nonconvex motion patterns. The extracted space-time regions allow for the detection and recognition of video events. Results of segmenting video content into static versus dynamic video regions and video content editing are presented.

Algorithms↗
PubMed2006

A time-space decomposition method for calculating the nearfield pressure generated by a pulsed circular piston.

A time-space decomposition approach is derived for numerical calculations of the transient nearfield pressure generated by a circular piston. Time-space decomposition analytically separates the temporal and spatial components of a rapidly converging single integral expression, thereby converting transient nearfield pressure calculations into the superposition of a small number of fast-converging spatial integrals that are weighted by time-dependent factors. Results indicate that, for the same peak error value, time-space decomposition is at least one or two orders of magnitude faster than the Rayleigh-Sommerfeld integral, the Schoch integral, the Field II program, and the DREAM program. Time-space decomposition is also faster than methods that directly calculate the impulse response by at least a factor of 3 for a 10% peak error and by a factor of 17 for a 1% peak error. The results show that, for a specified maximum error value, time-space decomposition is significantly faster than the impulse response and other analytical integrals evaluated for computations of transient nearfield pressures generated by circular pistons.

Computer Simulation↗
PubMedDate not supplied

Transferring of speech movements from video to 3D face space.

We present a novel method for transferring speech animation recorded in low quality videos to high resolution 3D face models. The basic idea is to synthesize the animated faces by an interpolation based on a small set of 3D key face shapes which span a 3D face space. The 3D key shapes are extracted by an unsupervised learning process in 2D video space to form a set of 2D visemes which are then mapped to the 3D face space. The learning process consists of two main phases: 1) Isomap-based nonlinear dimensionality reduction to embed the video speech movements into a low-dimensional manifold and 2) K-means clustering in the low-dimensional space to extract 2D key viseme frames. Our main contribution is that we use the Isomap-based learning method to extract intrinsic geometry of the speech video space and thus to make it possible to define the 3D key viseme shapes. To do so, we need only to capture a limited number of 3D key face models by using a general 3D scanner. Moreover, we also develop a skull movement recovery method based on simple anatomical structures to enhance 3D realism in local mouth movements. Experimental results show that our method can achieve realistic 3D animation effects with a small number of 3D key face models.

Algorithms↗
PubMed2004

LTB4 is present in exudative pleural effusions and contributes actively to neutrophil recruitment in the inflamed pleural space.

The pleural space is a virtual compartment between the lung and chest wall that becomes filled with fluid and inflammatory cells during a variety of respiratory diseases. Here, we study the potential role of the eicosanoid metabolite leukotriene B4 (LTB4) in disparate diseases leading to acute (pneumonia) or chronic (tuberculosis, cancer) inflammation of the pleural space. LTB4 concentrations were significantly higher in pleural fluid due to pneumonia, tuberculosis and cancer with respect to congestive heart failure and correlated with neutrophil elastase, which is used as an indication of state of activation of neutrophils in the pleural space. Moreover, pleural LTB4 was biologically active, as an anti-LTB4 antibody partially neutralized the chemotactic activity of parapneumonic, tuberculous and cancer effusions. Macrophages, neutrophils, lymphocytes, mesothelial cells and cancer cells all expressed mRNA for 5-lipoxygenase, the enzyme that initiates leukotriene synthesis leading to the production of LTB4, in exudative pleural effusions. Upon stimulation in transudative pleural effusions, pleural macrophages produced, in a time-dependent fashion, a significantly higher concentration of LTB4 than mesothelial cells. These studies demonstrate that different cell types are capable of producing LTB4 in the inflamed pleural space and that this mediator may play a crucial role in the recruitment of neutrophils into the pleural space.

Adult↗
PubMed2007

Spaced education improves the retention of clinical knowledge by medical students: a randomised controlled trial.

PURPOSE: Medical knowledge learned by trainees is often quickly forgotten. How can the educational process be tailored to shift learning into longer-term memory? We investigated whether 'spaced education', consisting of weekly e-mailed case scenarios and clinical questions, could improve the retention of students' learning. METHODS: During the 2004-5 surgery clerkships, 3rd-year students completed a mandatory 1-week clinical rotation in urology and validated web-based teaching programme on 4 core urology topics. Spaced educational e-mails were constructed on all 4 topics based on a validated urology curriculum. Each consisted of a short clinically relevant question or clinical case scenario in multiple-choice question format, followed by the answer, teaching point summary and explanations of the answers. Students were randomised to receive weekly e-mailed case scenarios in only 2 of the 4 urology topics upon completion of their urology rotation. Students completed a validated 28-item test (Cronbach's alpha = 0.76) on all 4 topics prior to and after the rotation and at the end of the academic year. RESULTS: A total of 95 of 133 students (71%) completed the end-of-year test. There were no significant differences in baseline characteristics between randomised cohorts. Spaced education significantly improved composite end-of-year test scores (P < 0.001, paired t-test). The impact of the spaced educational e-mails was largest for those students who completed their urology education 6-8 and 9-11 months previously (Cohen's effect sizes of 1.01 and 0.73, respectively). CONCLUSION: Spaced education consisting of clinical scenarios and questions distributed weekly via e-mail can significantly improve students' retention of medical knowledge.

Boston↗
PubMed1990

The Maturation of the Superior Collicular Map of Auditory Space in the Guinea Pig is Disrupted by Developmental Auditory Deprivation.

Guinea pigs, reared from birth in an environment of omnidirectional white noise, fail to develop a map of auditory space in the deeper layers of the superior colliculus. Collicular responses from such noise-reared animals reveal large auditory spatial receptive fields. The representation of auditory space in the colliculus shows no topographic order. Exposing developing animals to the noise environment only for restricted time periods showed that animals reared normally up to 26 days after birth (DAB) and then placed in the noise chamber could not construct spatial maps, whereas animals reared normally to 30 DAB and then placed in the noise chamber until the terminal mapping experiment could construct topographically organized spatial maps with local receptive fields. Limiting the noise exposure to the period between 26 and 30 DAB was sufficient to prevent spatial map formation. The failure to form a map of auditory space did not reflect environmental damage to the cochlea or the functional organization of the primary auditory pathway. The response thresholds of cochlear microphonics and of auditory responses in both the inferior and superior colliculus were normal in noise-reared animals. Similarly normal were the tonotopic organization and frequency tuning characteristics of inferior collicular neurons. The rearing environment thus appears to exert a selective effect upon the maturation of the superior collicular map of auditory space. We attribute this effect to the masking, by the omnidirectional broad-band noise, of discrete localized auditory stimuli. Cues deriving from these latter stimuli would appear to be necessary for the elaboration of the map of auditory space. This auditory experience operates during a 4 day crucial developmental period from 26 to 30 DAB. This is the same developmental time window as that during which visual experience is required for the construction of the map.

Journal Article↗
PubMed2000

Consumerism, disorientation and postmodern space: a modest test of an immodest theory.

There has recently been an explosion of theoretical literature on social space. A central claim in this literature is that postmodern spaces are experienced as confusing or disorienting by human subjects. This claim remains untested. The paper reports results from a small-scale survey conducted in one form of postmodern space--the shopping mall. It suggests that unsupported assertions about the disorienting effects of postmodern space and their associated influence on consumerist activities should be treated with scepticism. Through practice humans are able to develop routines which enable them to competently navigate these spaces.

Community Participation↗
PubMed2000

An in vitro comparison of 5 techniques for impressing dowel space preparations.

PURPOSE: This in vitro study compared 5 different dowel space impression techniques using polyvinyl siloxane impression material to determine which method produced fewer voids in the dowel space impression. MATERIALS AND METHODS: Five techniques were used to make impressions of a prepared dowel space in a simulated endodontically treated tooth. Technique I used a 25-gauge anesthetic needle to act as a vent at the apex of the preparation to reduce voids produced during the expression of light body impression material. The anesthetic needle was removed after the impression material was injected, and an impression post was then inserted to the depth of the preparation. Twenty impressions made using this technique were compared with other techniques that used the vent without a post, no vent with a post, no vent without a post, and a lentulo spiral with a post (Techniques II through V, respectively). The percentage of impressions with voids from each group was compared to determine which technique consistently produced a void-free impression of the complete preparation length. If voids were observed in the impression, the specimen was considered inadequate. RESULTS: The percents of void-free impressions using Techniques I through V were 100%, 70%, 40%, 60%, and 20%, respectively. CONCLUSIONS: Using a 25-gauge needle as a vent while expressing impression material into the dowel space followed by placing the impression post consistently produced void-free dowel space impressions.

Dental Impression Materials↗
PubMedDate not supplied

Indications, surgical technique, and long-term experience with laparoscopic closure of the nephrosplenic space in standing horses.

OBJECTIVE: To describe surgical technique and outcome after laparoscopic closure of the nephrosplenic space for treatment of recurrent left dorsal displacement of the left colon (LDDLC) in standing horses. STUDY DESIGN: Retrospective study. ANIMALS: Forty-four horses with LDDLC. METHODS: Laparoscopic portals were located in the left flank region. After administration of etilefrin intravenously to contract the spleen, the dorsal splenic margin was sutured to the nephrosplenic ligament to obliterate the nephrosplenic space. Horses were re-examined (< or = 3 years) for history of recurrence. In addition, medical records of 4,852 horses treated for colic over 16 years were evaluated to establish incidence of LDDLC and recurrence after treatment. RESULTS: Splenic contraction facilitated suture placement and closure of the nephrosplenic space was achieved without complications. LDDLC recurrence did not occur although 5 horses had subsequent episodes of colic; 4 horses had displacement of the ascending colon between the spleen and body wall. Review of medical records revealed an incidence of LDDLC of 6% and recurrence of 21% in a population of horses with signs of colic. CONCLUSION: Laparoscopic closure of the nephrosplenic space, facilitated by etilefrin-induced splenic contraction can be efficiently performed in standing horses. CLINICAL RELEVANCE: Laparoscopic ablation of the nephrosplenic space should be considered in horses that are predisposed to recurrent LDDLC.

Animals↗
PubMed2006

Laparoscopic obliteration of the nephrosplenic space using polypropylene mesh in five horses.

OBJECTIVE: To report a laparoscopic technique for insertion of polypropylene mesh in the nephrosplenic space in horses and evaluate outcome. STUDY DESIGN: Descriptive experimental study. ANIMALS: Five healthy mature horses. METHODS: One laparoscope and 2 instrument portals were made on the left side of the horse. The nephrosplenic space was measured and appropriately sized polypropylene mesh was inserted and attached to the dorsolateral splenic capsule and perirenal fascia using helical titanium coils. All horses had repeat laparoscopy 4 weeks later and were necropsied at intervals 4-14 weeks after mesh placement. RESULTS: Mean time for laparoscopic mesh placement was 104 minutes. None of the horses had signs of colic and at 4 weeks all mesh implants were covered by fibrous tissue. One horse had a descending colon mesenteric adhesion to the mesh. At necropsy, the fibrous tissue covering the mesh had adhered to itself and pulled the splenic capsule and perirenal fascia into close apposition. Each mesh implant was firmly adhered to the spleen, nephrosplenic ligament, and perirenal fascia. CONCLUSIONS: Laparoscopic mesh placement was easily performed, well tolerated, and provided excellent fibrous obliteration of the nephrosplenic space. The single important complication observed was a mesenteric adhesion of the descending colon to the mesh in 1 horse. CLINICAL RELEVANCE: Laparoscopic placement of polypropylene mesh leads to obliteration of the nephrosplenic space within 4 weeks and should prevent entrapment of viscera in the nephrosplenic space.

Animals↗
PubMed1999

Double pulse transthoracic defibrillation in the calf using percent fibrillation cycle length as spacing determinate.

Recent studies have found that when multiple pulses of energy are used for defibrillation with implantable electrodes, the spacing between these pulses is better determined as a percentage of the fibrillation cycle length (CL), rather than as a fixed function of time. Here, this concept is further tested in the transthoracic defibrillation of calves, which are approximately the size of heavy humans. Eleven 90-110 kg calves (101 +/- 6 kg) were used in evaluating the effectiveness in achieving transthoracic ventricular defibrillation of ten double pulse waveforms (two 50 A 4-ms rectangular monopulses) having leading edge-to-edge spacings of 4 ms (a 50 A 8-ms rectangular monopulse) and 50, 60, 70, 80, 90, 100, 110, 120, 130 percent fibrillation CL, respectively. In each of these waveforms, the total time when 50 A current was flowing (on time) was 8 ms. Our results show an unequivocal adverse interaction between the pulses, when the spacing is around 60%-70% fibrillation CL; but that the two pulses combined to defibrillate as effectively as a single 8-ms pulse when the spacing is around 110%-130% fibrillation CL. Electrocardiographic analysis suggests that the adverse interaction is due to a refibrillation phenomenon. This study confirms that double pulses can interact and have a negative effect on defibrillation efficacy. Our data suggests that the mechanism of this interaction involves the second pulse reinitiating fibrillation when the pulse separation is in a critical range of values. Our results are also compatible with the hypothesis that the spacing of multiple pulses is better determined as a percentage of the fibrillation CL than as absolute time, although more study is necessary to fully test this hypothesis.

Animals↗
PubMed1997

Corrosion casts of the suprachoroidal space and uveoscleral drainage routes in the human eye.

Human cadaver eyes were studied by corrosion casting technique. Batson's mixture No. 17 (methyl methacrylate) was injected through a sclerotomy into the suprachoroidal space. Following polymerisation of the injected mixture the surrounding tissue was dissolved with 10% natrium hydroxide. Macroscopic and scanning electron microscopic findings in casts of the suprachoroidal space are presented. Due to transscleral drainage of resin from the suprachoroidal space, different types of branches deriving from the outer (scleral) surface of the casts were found. Some of these branches corresponded to the perivascular spaces of both ciliary vessels and vortex veins. In addition, we found branches probably representing channels deriving directly from the suprachoroidal space, communicating with the intrascleral venous plexus. Such channel systems have previously not been described, and their possible relation to the uveoscleral drainage of aqueous humour is discussed.

Aged↗
PubMed1994

Tooth spaces in and prosthetic treatment received by the middle-aged and the elderly in Hong Kong.

The purpose of this study was to describe the state of the dentition of middle-aged and elderly Chinese in Hong Kong in terms of teeth present, tooth spaces, and prosthetic treatment received. In an oral health survey conducted in 1991 in Hong Kong, a sample of 372 35-44-yr-olds and 537 noninstitutionalized 65-74-yr-olds was interviewed and clinically examined. In all dentate subjects, each tooth was scored for the presence/absence of that tooth, a tooth space of 5.5 mm which had not been treated, or the presence of a denture or pontic replacing that tooth. Each denture was assessed according to a set of criteria. None of the 35-44-yr-olds were edentulous and the mean number of teeth present was 27.5. About 40% of the third molars and about 35% of the mandibular first molars were missing. For only 1% of the missing teeth had space closure resulted in missing teeth not being recorded as tooth spaces or treated tooth spaces. Overall, 72% of the 35-44-yr-olds had no prosthesis, 17% had a bridge or bridges, 12% had a denture or dentures, and 1% had both. Of the 65-74-yr-olds, 12% were edentulous, and the dentate subjects had a mean number of 17 teeth present. About 70% of the molars were missing. Overall, only 29% of the elderly had no prosthesis, 52% had a denture or dentures, 33% had a bridge or bridges, and 13% had both. Only 35% and 28%, respectively, of the middle-aged and elderly denture wearers had no complaint about their dentures.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMedDate not supplied

Changes in the canine femoropatellar joint space in the postsurgical, cruciate-deficient stifle joint.

In this study, we investigate the factors that influence changes in articular cartilage thickness in naturally occurring osteoarthritis of the canine stifle joint. Fifty-eight dogs with QA secondary to cranial cruciate ligament deficiency were examined radiographically at 0, 7, and 13 months using 90 degree flexed mediolateral radiographs of both stifle joints. The femoropatellar joint space widths were measured using a computer-assisted video image analysis system. The femoropatellar joint space widths were found to be significantly increased in index joints as compared to contralateral joints. In addition, there was a significant increase in femoropatellar joint space (FPJS) width over the course of the study, particularly between entry and 7 months. Factors that might influence the degree of femoropatellar joint space increase (bodyweight, age, sex, disease duration, radiographic score) were investigated using regression analysis. Body weight at baseline showed a moderate to strong relationship with change in FPJS between 0 and 7 months (Pearson's partial correlation r = 0.417, p = .006). This relationship was less strong for change in femoropatellar joint space between 7 and 13 months (r = 0.324, p = .036).

Animals↗
PubMed1986

The stiffness of frog skinned muscle fibres at altered lateral filament spacing.

When the surface membrane is removed from a frog muscle fibre the myofibrils swell, so that the spacing between the filaments increases by 10-30%. In this study, the stiffness of skinned fibres was measured when the lateral spacing of the filament lattice was reduced osmotically using polyvinyl pyrrolidone (PVP), a synthetic linear polymer. In the absence of PVP, the apparent stiffness of relaxed skinned fibres measured during ramp stretches was about 0.05-0.1 of the stiffness of intact fibres. The stiffness increased when the lattice spacing was decreased. The mechanical characteristics of resting stiffness in the presence of PVP (or bovine serum albumin) were similar to those of the short-range elastic component of resting intact fibres. However, when the spacing of skinned fibres was reduced osmotically to that of the intact lattice, the stiffness of skinned fibres was about 1.6 times higher. In the absence of PVP, Ca2+-activated skinned fibres were less stiff than are fully active intact fibres during isometric tetani. The skinned fibre force-extension relation was markedly curved. As the filament spacing was reduced, the stiffness of the Ca2+-activated skinned fibres increased, with little change in isometric tension, and the force-extension curve became more linear. Experiments at varied filament overlap and during feed-back control of sarcomere length, monitored by laser diffraction, showed that PVP increased the stiffness of the sarcomeres. The increase of active stiffness in the presence of PVP could be partially dissociated from the increase of resting stiffness by inclusion of Mg tripolyphosphate in the bathing solutions. It is concluded that the low stiffness and the non-linearity of the force-extension curve observed in fully activated skinned fibres are due primarily to the increase of filament separation that occurs when a fibre is skinned. The mechanism may be related to an increased angle between the subfragment-2 part of the cross-bridge and the backbone of the thick filament, perhaps leading to buckling of cross-bridges under compression.

Actin Cytoskeleton↗
PubMed2006

Towards a theory of a solution space for the biplane imaging geometry problem.

Biplane angiographic imaging is a primary method for visual and quantitative assessment of the vasculature. In order to reliably reconstruct the three-dimensional (3D) position, orientation, and shape of the vessel structure, a key problem is to determine the rotation matrix R and the translation vector t which relate the two coordinate systems. This so-called Imaging Geometry Determination problem is well studied in the medical imaging and computer vision communities and a number of interesting approaches have been reported. Each such technique determines a solution which yields 3D vasculature reconstructions with errors comparable to other techniques. From the literature, we see that different techniques with different optimization strategies yield reconstructions with equivalent errors. We have investigated this behavior, and it appears that the error in the input data leads to this equivalence effectively yielding what we call the solution space of feasible geometries, i.e., geometries which could be solutions given the error or uncertainty in the input image data. In this paper, we lay the theoretical framework for this concept of a solution space of feasible geometries using simple schematic constructions, deriving the underlying mathematical relationships, presenting implementation details, and discussing implications and applications of the proposed idea. Because the solution space of feasible geometries encompasses equivalent solutions given the input error, the solution space approach can be used to evaluate the precision of calculated geometries or 3D data based on known or estimated uncertainties in the input image data. We also use the solution space approach to calculate an imaging geometry, i.e., a solution.

Algorithms↗
PubMed1999

An analytical model of a kilovoltage beam phase space.

Our aim in this project was to quantify a kilovoltage beam phase space for use in dose calculations. The phase space was modeled by incorporating the following analytically derived x-ray beam production properties: the intensity variation due to the heel effect, the energy variation due to the differing amount of target material traversed by the photons, and the finite source size. The initial energy spectrum used was generated using a computer program. A Monte Carlo code was adapted in order to examine the validity of the calculated phase space. Dose distributions calculated using the modeled phase space for 10x10 and 20x20 cm2 fields show agreement with experimental values to within 2% and 4%, respectively, for the central 80% of the field size. Within the field but outside this range a maximum of 6% difference (for the 20x20 cm2 field) was observed, however, these values were in a region of sharp gradient and hence small geometric shift. The "tails" of the profiles were underpredicted by up to 6%. Due to uncertainties in experiment (3%) and Monte Carlo (1.5%), the modeled phase space is deemed acceptable for phantom and in-vivo dosimetric calculations within the field boundaries.

Biophysical Phenomena↗