New proposal for closed-string field theory: The free-string case.
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Journal Article↗
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Space time singularities in string theory and string propagation through gravitational shock waves.
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Journal Article↗
N=4 string is the same as the N=2 string.
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Absence of open strings in a lattice-free simulation of cosmic string formation.
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Journal Article↗
Heart strings and purse strings: Carryover effects of emotions on economic decisions.
We examined the impact of specific emotions on the endowment effect, the tendency for selling prices to exceed buying or "choice" prices for the same object. As predicted by appraisal-tendency theory, disgust induced by a prior, irrelevant situation carried over to normatively unrelated economic decisions, reducing selling and choice prices and eliminating the endowment effect. Sadness also carried over, reducing selling prices but increasing choice prices--producing a "reverse endowment effect" in which choice prices exceeded selling prices. The results demonstrate that incidental emotions can influence decisions even when real money is at stake, and that emotions of the same valence can have opposing effects on such decisions.
Adolescent↗
Asymmetries in perception of tachistoscopically presented horizontal and vertical random-letter strings.
Two studies examined perception of briefly presented (100-msec.) strings of letters. In Study One, 20 subjects were presented horizontal 5-letter strings in the left, central, and right visual fields. These were compared with 5-letter vertical strings presented centrally in the lower, central, and upper visual fields. Similar within-string patterns were found for all presentations. Between strings there was a typical right over left visual-field advantage in accuracy of report for horizontal strings. There was no equivalent lower over upper visual-field advantage for vertical strings. In Study Two, 24 subjects were presented vertical strings in the right and left visual fields, vertical strings in the upper and lower visual fields, and horizontal strings in the right and left visual fields. A post-stimulus cueing technique for single letters was used. Between-strings, the same right over left visual-field advantage for horizontal strings was noted but not for vertical strings. Between strings no advantage for lower over upper visual fields was found. An interaction for within-string patterns and visual field was found for vertical strings presented in the upper and lower visual fields. These results are explained in terms of an interaction between scanning and masking effects depending upon orientation and visual field.
Adult↗
Radial artery angiographic string sign: clinical consequences and the role of pharmacologic therapy.
BACKGROUND: The radial artery is an increasingly important graft for coronary artery bypass surgery. Postoperative angiographic studies have shown that a proportion of radial grafts become diffusely narrowed but not occluded, or string signs. METHODS: Four hundred forty patients receiving a radial artery graft enrolled in a large clinical trial underwent postoperative angiography at 1 year. Angiograms were analyzed visually and quantitatively. A complete string sign was defined as diffuse narrowing along the full length of the graft, while a partial string sign was defined as segmental narrowing. Angiographic findings were correlated with medication compliance and clinical sequelae. RESULTS: Thirty-one patients (7.0 %) had radial artery graft string signs versus 4 patients (0.9%) with a saphenous vein graft string sign (p = 0.001). Complete string signs were present in 28 cases, and the mean diameter was 0.76 +/- 0.14 mm (mean +/- SD), whereas 3 cases had a partial string sign with a diameter of 0.89 +/- 0.14 mm. Fifteen radial arteries showed Thrombolysis in Myocardial Infarction Study (TIMI) 1 flow, 3 cases showed TIMI 2 flow, and 13 cases showed TIMI 3 flow. There was no difference in incidence of radial string sign between patients taking nifedipine versus diltiazem postoperatively. Multivariate analysis revealed the presence of radial artery string sign was closely related to the perioperative use of alpha-adrenergic agonists and target vessels stenosis less than 90%. Postoperative symptoms were associated with radial artery string signs with TIMI 1 flow (p = 0.0045). CONCLUSIONS: In the Radial Artery Patency Study, radial artery string sign was present in 7% of patients. Despite diffuse narrowing, 52% of grafts had TIMI 2 flow or better.
Adrenergic alpha-Agonists↗
A three-dimensional study of brain string vessels using celloidin sections stained with anti-collagen antibodies.
The purpose of this study was to explain the morphology and significance of string vessels in human brains. Brain slices (1.5 cm thick) were embedded in celloidin, sections cut at 100 microm and stained with antibody to collagen IV. A second component of the study was a 3-D rotational study for which we used sections stained with propidium iodide for cell nuclei and anti-collagen stain for blood vessel basement membranes. The materials consisted of brain from two infants at 28 and 35 weeks gestation, two term infants at 20 days and 3 months, one 5 years old, and 3 adults aged 25, 57, and 84 years. String vessels were counted in at least six fields of deep white matter using a 10x objective and the counts averaged and expressed as string vessels per cubic mm. The 3-D rotational study using confocal microscopy was designed to find nuclei in string vessels. The least number of string vessels were present in the premature infant. All others had comparably similar numbers of string vessels except the two term-born infants in whom there was a 3-5-fold increase. However, the two brains had other pathologic lesions, which could affect the counts. In normal brains, string vessels appear as a singe line of stain and usually connect two arterioles or capillaries. They can form loops and occasionally a string vessel may continue into a normal capillary. String vessels have rare nuclei. Our study indicates that string vessels are present in utero, increase in number and are present throughout life. Their exact nature remains unexplained. They apparently do not represent age-related acquired atrophy of capillaries because they are present at all ages and do not progressively increase with normal aging. This technique appears suitable for the study of large number of string vessels.
Adult↗
Dogs (Canis lupus familiaris) fail to show understanding of means-end connections in a string-pulling task.
Domestic dogs (Canis lupus familiaris) were tested in four experiments for their understanding of means-end connections. In each of the experiments, the dogs attempted to retrieve a food treat that could be seen behind a barrier and which was connected, via string, to a within-reach wooden block. In the experiments, either one or two strings were present, but the treat was attached only to one string. Successful retrieval of the treat required the animals to pull the appropriate string (either by pawing or by grasping the wooden block in their jaws) until the treat emerged from under the barrier. The results showed that the dogs were successful if the treat was in a perpendicular line to the barrier, i.e. straight ahead, but not when the string was at an angle: in the latter condition, the typical response was a proximity error in that the dogs pawed or mouthed at a location closest in line to the treat. When two strings that crossed were present, the dogs tended to pull on the wrong string. The combined results from the experiments show that, although dogs can learn to pull on a string to obtain food, they do not spontaneously understand means-end connections involving strings.
Animals↗
Short superstrings and the structure of overlapping strings.
Given a collection of strings S = [s1,...,sn] over an alphabet sigma, a superstring alpha of S is a string containing each si as a substring, that is, for each i, 1 < or = i < or = n, alpha contains a block of magnitude of si consecutive characters that match si exactly. The shortest superstring problem is the problem of finding a superstring alpha of minimum length. The shortest superstring problem has applications in both computational biology and data compression. The shortest superstring problem is NP-hard (Gallant et al., 1980); in fact, it was recently shown to be MAX SNP-hard (Blum et al., 1994). Given the importance of the applications, several heuristics and approximation algorithms have been proposed. Constant factor approximation algorithms have been given in Blum et al. (1994) (factor of 3), Teng and Yao (1993) (factor of 2 8/9), Czumaj et al. (1994) (factor of 2 5/6), and Kosaraju et al. (1994) (factor of 2 50/63). Informally, the key to any algorithm for the shortest superstring problem is to identify sets of strings with large amounts of similarity, or overlap. Although the previous algorithms and their analyses have grown increasingly sophisticated, they reveal remarkably little about the structure of strings with large amounts of overlap. In this sense, they are solving a more general problem than the one at hand. In this paper, we study the structure of strings with large amounts of overlap and use our understanding to give an algorithm that finds a superstring whose length is no more than 2 3/4 times that of the optimal superstring. Our algorithm runs in O(magnitude of S + n3) time, which matches that of previous algorithms. We prove several interesting properties about short periodic strings, allowing us to answer questions of the following form: Given a string with some periodic structure, characterize all the possible periodic strings that can have a large amount of overlap with the first string.
Algorithms↗
Implications of the angiographic string sign in carotid atherosclerosis.
We identified 60 patients (42 men and 18 women with an average age of 62.6 years) with angiographically documented carotid stenoses of greater than or equal to 95%; a string sign was demonstrated in 28. Twenty of the 60 patients (33%) were asymptomatic on presentation, 26 (43%) had hemispheric transient ischemic attacks, 21 (35%) had amaurosis fugax, and nine (15%) had previous ipsilateral infarctions. Demographics, mode of presentation, and prevalence of atherosclerotic risk factors were not significantly different between patients with and without a string sign. Doppler frequencies recorded in patients with a string sign were less than 6 or greater than 16 KHz. Real-time ultrasonography imaged a patent lumen in all but three cases with a string sign. Surgery was performed in 26 patients with a string sign and in 21 patients without a string sign. The rate of major perioperative complications was not influenced by the presence of a string sign, contralateral extracranial stenosis, or ipsilateral siphon stenosis. Average lumen size of the endarterectomy specimens was 0.94 mm in those with and 1.7 mm in those without a string sign. We conclude that combined noninvasive testing has a sensitivity of 83% for demonstrating a residual lumen in patients with greater than or equal to 95% carotid stenosis and that the angiographic string sign does not affect the mode of presentation or surgical outcome of these patients.
Aged↗
Transcriptional regulation of string (cdc25): a link between developmental programming and the cell cycle.
During postblastoderm embryogenesis in Drosophila, cell cycles progress in an invariant spatiotemporal pattern. Most of these cycles are differentially timed by bursts of transcription of string (cdc25), a gene encoding a phosphatase that triggers mitosis by activating the Cdc2 kinase. An analysis of string expression in 36 pattern-formation mutants shows that known patterning genes act locally to influence string transcription. Embryonic expression of string gene fragments shows that the complete pattern of string transcription requires extensive cis-acting regulatory sequences (> 15.3 kb), but that smaller segments of this regulatory region can drive proper temporal expression in defined spatial domains. We infer that string upstream sequences integrate many local signals to direct string's transcriptional program. Finally, we show that the spatiotemporal progression of string transcription is largely unaffected in mutant embryos specifically arrested in G2 of cycles 14, 15, or 16, or G1 of cycle 17. Thus, there is a regulatory hierarchy in which developmental inputs, not cell cycle inputs, control the timing of string transcription and hence cell cycle progression.
Animals↗
Particle dynamics and the development of string-like motion in a simulated monoatomic supercooled liquid.
The microscopic details of local particle dynamics is studied in a glass-forming one component supercooled liquid modeled by a Dzugutov potential developed for simple metallic glass formers. Our main goal is to investigate particle motion in the supercooled liquid state, and to ascertain the extent to which this motion is cooperative and occurring in quasi-one-dimesional, string-like paths. To this end we investigate in detail the mechanism by which particles move along these paths. In particular, we show that the degree of coherence--that is, simultaneous motion by consecutive particles along a string--depends on the length of the string. For short strings, the motion is highly coherent. For longer strings, the motion is highly coherent only within shorter segments of the string, which we call "microstrings." Very large strings may contain several microstrings within which particles move simultaneously, but individual microstrings within a given string are temporally uncorrelated with each other. We discuss possible underlying mechanism for this complex dynamical behavior, and examine our results in the context of recent work by Garrahan and Chandler [Phys. Rev. Lett. 89, 035704 (2002)] in which dynamic facilitation plays a central role in the glass transition.
Journal Article↗
False beats in coupled piano string unisons.
The behavior of a unison pair of piano strings coupled by the soundboard bridge, when one string has localized anisotropy in the reactive part of the bridge admittance for a given partial frequency, can be investigated using a theoretical matrix description. The anisotropy can cause what in piano tuning terminology is referred to as "false beating" in a partial of the single string. A mathematical model can be used to illustrate how "mistunings" between the strings of the unison (measured when the strings are sounding in isolation from each other) may theoretically arise as a consequence of the normal practice in piano tuning, of eliminating or reducing audible beating in the unison when both strings are sounding. "False beats" in a single string partial can be "inherited" by a partial of the coupled unison's spectrum, and mistunings between the strings can eliminate or reduce the appearance of this inheritance.
Anisotropy↗
Validation of string test for diagnosis of Helicobacter pylori infections.
The method of recovering Helicobacter pylori DNA or viable cells absorbed on a string that a person has swallowed and that is retrieved an hour later (string test) should be a useful alternative to traditional analysis of cells or DNA obtained by endoscopy, which is invasive, uncomfortable, relatively costly, and ill-suited for community-based and pediatric studies. Here we assayed the sensitivity and validity of the string test versus conventional endoscopic biopsy for detecting and analyzing H. pylori infection. Forty-four people with gastric complaints were studied using both H. pylori culture and urease gene (ureB) PCR. H. pylori organisms cultured from strings and biopsy specimens from the same patients were fingerprinted by the randomly amplified polymorphic DNA (RAPD) method. Biopsy sections were also hematoxylin and eosin and silver stained for H. pylori detection. H. pylori was cultured from 80% of strings and detected by PCR from 91% of strings from participants whose biopsies had been H. pylori positive by culture, PCR, and/or histology. Strains recovered from strings and biopsy specimens yielded identical or closely related RAPD profiles in each of the 24 cases tested. We conclude that the string test is a useful method for H. pylori recovery and analysis when relatively noninvasive procedures are needed.
Adult↗
Emerging neurophysiological specialization for letter strings.
In adult readers, printed words and other letter strings activate specialized visual functions within 200 msec, as evident from neurophysiological recordings of brain activity. These fast, specialized responses to letter strings are thought to develop through plastic changes in the visual system. However, it is unknown whether this specialization emerges only with the onset of word reading, or represents a precursor of literacy. We compared 6-year-old kindergarten children who could not yet read words to adult readers. Both age groups detected immediate repetitions of visually presented words, pseudowords, symbol strings, and pictures during event-related potential (ERP) mapping. Maps from seven corresponding ERP segments in children and adults were analyzed regarding fast (<250 msec) and slow (>300 msec) specialization for letter strings. Adults reliably differentiated words through increased fast (<150 msec) occipito-temporal N1 activity from symbols. Children showed a later, more mid-occipital N1 with marginal word-symbol differences, which were absent in those children with low letter knowledge. Children with high letter knowledge showed some fast sensitivity to letter strings, which was confined to right occipito-temporal sites, unlike the stronger adult N1 specialization. This suggests that a critical degree of early literacy induces some immature, but fast, specialization for letter strings before word reading becomes possible. Children also differentiated words from symbols in later segments through increased right occipito-temporal negativity for words. This slow specialization for letter strings was not modulated by letter knowledge and was absent in adults, possibly reflecting a visual precursor of literacy due to visual familiarity with letter strings.
Adult↗
A G-string positive cis-regulatory element in the LpS1 promoter binds two distinct nuclear factors distributed non-uniformly in Lytechinus pictus embryos.
The LpS1 alpha and beta genes of Lytechinus pictus are activated at the late cleavage stage of embryogenesis, with LpS1 mRNAs accumulating only in lineages contributing to aboral ectoderm. We had shown previously that 762 bp of 5' flanking DNA from the LpS1 beta gene was sufficient for proper temporal and aboral ectoderm specific expression. In the present study, we identified a strong positive cis-regulatory element at -70 bp to -75 bp in the LpS1 beta promoter with the sequence (G)6 and a similar, more distal cis-element at -721 bp to -726 bp. The proximal 'G-string' element interacted with two nuclear factors, one specific to ectoderm and one to endoderm/mesoderm nuclear extracts, whereas the distal G-string element interacted only with the ectoderm factor. The ectoderm and endoderm/mesoderm G-string factors were distinct based on their migratory behavior in electrophoretic mobility shift assays, binding site specificities, salt optima and EDTA sensitivity. The proximal G-string element shared homology with a binding site for the mammalian transcription factor IF1, a protein that binds to negative cis-regulatory elements in the mouse alpha 1(I) and alpha 2(I) collagen gene promoters. Competition experiments using wild-type and mutant oligonucleotides indicated that the ectoderm G-string factor and IF1 have similar recognition sites. Partially purified IF1 specifically bound to an oligonucleotide containing the proximal G-string of LpS1 beta. From our results, we suggest that the ectoderm G-string factor, a member of the G-rich DNA-binding protein family, activates the LpS1 gene in aboral ectoderm cells by binding to the LpS1 promoter at the proximal G-string site.
Animals↗
Breath and string test: a diagnostic package for the identification of treatment failure and antibiotic resistance of Helicobacter pylori without the necessity of upper gastrointestinal endoscopy.
AIM: Helicobacter pylori (H pylori) resistance after failed eradication has a major impact on the outcome of a further treatment regimen. The aim of this study was to assess the validity of a non-invasive strategy using the 13C-urea breath test (UBT) and the gastric string test in identifying post-treatment resistance of H pylori. METHODS: The UBT was routinely performed 4 to 6 wk after H pylori eradication therapy. Forty-two patients (24 females, 18 males, mean age 48 years) with a positive UBT were included in the study. A gastric string test using a capsule containing a 90 cm-long nylon fiber was performed. Before the capsule was swallowed, the free end of the string was taped to the cheek. After one hour in the stomach, the string was withdrawn. The distal 20 cm of the string was inoculated onto an agar plate and processed under micro-aerophilic conditions. Following the string test, upper gastrointestinal endoscopy was performed to obtain gastric biopsies for conventional culture. RESULTS: H pylori was successfully cultured from the gastric string in 34 patients (81%), but not in 5 patients due to contamination with oropharyngeal flora. H pylori was cultured from the gastric biopsies obtained at endoscopy in 39 patients (93%). CONCLUSION: The UBT followed by the gastric string test in the case of treatment failure is a valid diagnostic strategy with the aim of determining the post-therapeutic antibiotic resistance of H pylori with little inconvenience to the patient. Upper GI-endoscopy can be avoided in several cases by applying consequently this diagnostic package.
Anti-Bacterial Agents↗