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PubMed2005

Theoretical mechanics: crowd synchrony on the Millennium Bridge.

Soon after the crowd streamed on to London's Millennium Bridge on the day it opened, the bridge started to sway from side to side: many pedestrians fell spontaneously into step with the bridge's vibrations, inadvertently amplifying them. Here we model this unexpected and now notorious phenomenon--which was not due to the bridge's innovative design as was first thought--by adapting ideas originally developed to describe the collective synchronization of biological oscillators such as neurons and fireflies. Our approach should help engineers to estimate the damping needed to stabilize other exceptionally crowded footbridges against synchronous lateral excitation by pedestrians.

Biological Clocks↗
PubMed1987

Mandibular anterior crowding and periodontal disease.

A short-term longitudinal study of the role of mandibular anterior crowding in inflammatory periodontal diseases. Crowded dentitions show more periodontal involvement, and the improvement after scaling disappears more rapidly.

Adult↗
PubMed1994

Crowding: timing of treatment.

The late mixed dentition stage of development, after the eruption of the first premolars, is a favorable time to start treatment to resolve crowding. This protocol offers the clinician choices. If nonextraction treatment is preferable, arch length preservation can provide the space for alignment in approximately 75% of all patients with crowding. If extraction treatment is indicated, the first premolars are available.

Bicuspid↗
PubMed1997

Occlusal relationships and spacing or crowding of teeth in the dentitions of 3-4-year-old Nigerian children.

A study of 525 3-4-year-old children in nursery schools and day-care centres was carried out to assess occlusal relationships and the presence of spacing or crowding of teeth. No significant differences in occlusal relationships were found between boys and girls (P > 0.05). Bilateral straight terminal planes of molars and class 1 canine relationship were the most prevalent features (74.5% and 73.3% respectively). Most of the children had 'normal' vertical and transverse occlusal relationships. The most common sites of spacing were mesial to maxillary canines and distal to mandibular canines. 32% of the children were found to have generalized anterior segment spacing, 4% showed exclusively anthropoid spaces, and 18% had either contact between all the teeth or crowding in the anterior region.

Chi-Square Distribution↗
PubMed2001

Ultracentrifugal studies of the effect of molecular crowding by trimethylamine N-oxide on the self-association of muscle glycogen phosphorylase b.

The suitability of sedimentation equilibrium for characterizing the self-association of muscle glycogen phosphorylase b has been reappraised. Whereas sedimentation equilibrium distributions for phosphorylase b in 40 mM Hepes buffer (pH 6.8) supplemented with 1 mM AMP signify a lack of chemical equilibrium attainment, those in buffer supplemented additionally with potassium sulfate conform with the requirements of a dimerizing system in chemical as well as sedimentation equilibrium. Because the rate of attainment of chemical equilibrium under the former conditions is sufficiently slow to allow resolution of the dimeric and tetrameric enzyme species by sedimentation velocity, this procedure has been used to examine the effects of thermodynamic nonideality arising from molecular crowding by trimethylamine N-oxide on the self-association behaviour of phosphorylase b. In those terms the marginally enhanced extent of phosphorylase b self-association observed in the presence of high concentrations of the cosolute is taken to imply that the effects of thermodynamic nonideality on the dimer-tetramer equilibrium are being countered by those displacing the T<==>R isomerization equilibrium for dimer towards the smaller, nonassociating T state. Because the R state is the enzymically active form, an inhibitory effect is the predicted consequence of molecular crowding by high concentrations of unrelated solutes. Thermodynamic nonideality thus provides an alternative explanation for the inhibitory effects of high concentrations of glycerol, sucrose and ethylene glycol on phosphorylase b activity, phenomena that have been attributed to extremely weak interaction of these cryoprotectants with the T state of the enzyme.

Animals↗
PubMed2003

Coping with a crowded ED: an expanded unique role for midlevel providers.

Crowding in the emergency department (ED) has multiple causes, including space and staffing in both inpatient areas and the ED. Waiting for inpatient beds is the primary issue in our ED. Waiting inpatients require continuing care and attention from emergency-medicine (EM) physicians. As a managerial response, we developed a unique role for midlevel practitioners (MLPs) in which they could provide "back-end" work for patients awaiting inpatient beds. After initial EM physician evaluation, patients without ready inpatient beds were grouped in the ED and their care was transferred to the transition team (TT). The TT consisted of an MLP (nurse practitioner or physician assistant) and a registered nurse or licensed practical nurse, all reporting to ED supervisors. MLPs were readily available from the local medical professional market. The TT provided all patient care until a patient was seen by the admitting inpatient service or until the patient left for an inpatient unit. The major TT objectives were a reduction of EM physician work in caring for inpatients, and improved patient care. We demonstrated that the TT assumed a significant patient load, an indirect measure of reduced EM physician work, but this did not improve patient satisfaction. The TT clinical role is less desirable to MLPs than are other traditional clinical roles. The TT is a potentially available, incremental staffing resource for a crowded ED.

Continuity of Patient Care↗
PubMed1982

[A new test (C-test) for quantitative examination of crowding with test results in amblyopic and ametropic patients (author's transl)].

A new acuity test was developed with a defined space between symbols to determine the effect of crowding on visual line acuity. Landolt-C was used as a symbol and the space between symbols (either 2 to 3 min. of arc or 17 to 18 min. of arc) was kept constant for all acuity values. The test permits a quantitative examination of crowding phenomena. The experimental results obtained in measurements of visual line acuity in normal-sighted, amblyopic and ametropic subjects are presented. The results of treatment for amblyopia had evidently been interpreted too optimistically in many patients hitherto.

Adult↗
PubMed2000

Effect of serial extraction alone on crowding: spontaneous changes in dentition after serial extraction.

We examined changes in dentition after serial extraction in subjects who wore no appliances to determine the relationships between changes in dentition and improvement in dental crowding. Mandibular dental casts and lateral cephalograms from 31 subjects who had undergone serial extraction without orthodontic treatment were analyzed at 3 stages: before extraction of the deciduous canines (T1), after extraction of first premolars (T2), and at the end of the observation period (T3). Although movements of the first molar cusp and apex from T2 to T3 were significantly greater than from T1 to T2, movements of the incisor cusp and apex from T1 to T2 were significantly greater than from T2 to T3. The first molar tipped mesially from T1 to T2 but tipped distally from T2 to T3. The distal tipping of the incisor from T1 to T2 was significantly greater than from T2 to T3. These results suggest that the main changes in dentition from T1 to T2 are different from those from T2 to T3. The correlations between the annual change in the canine movement or tipping from T2 to T3 and the annual change in the irregularity index at the same time were significant. These results suggest that the canine movement or tipping contributed to the correction of the anterior crowding from T2 to T3.

Analysis of Variance↗
PubMed2000

Short-term effects of fiberotomy on relapse of anterior crowding.

The effects of fiberotomy were evaluated in alleviating dental relapse of incisors after orthodontic treatment. The study sample consisted of 23 patients with crowded maxillary and mandibular incisors before orthodontic treatment. The amount of initial crowding was determined according to Little's irregularity index. Fiberotomy procedures were performed on 11 of the patients 1 week before debonding. The other 12 subjects served as the control group. All patients wore Hawley retainers. Lateral cephalometric headfilms and dental casts of the patients were taken at the beginning (T1) and at the end (T2) of treatment, 6 months into the retention phase (T3), and 1 year after orthodontic treatment (T4). Significant increase of irregularity index was noted in the control group at T3 and T4 for both maxillary and mandibular anterior segments (P <.05, P <.01). Meanwhile, in the group where circumferential supracrestal fiberotomy was performed, no significant increase of the irregularity index was noted.

Adolescent↗
PubMed2005

Adaptation to spiral motion in crowding condition.

When a single, moving stimulus is presented in the peripheral visual field, its direction of motion can be easily distinguished, but when the same stimulus is flanked by other similar moving stimuli, observers are unable to report its direction of motion. In this condition, known as 'crowding', specific features of visual stimuli do not access conscious perception. The aim of this study was to investigate whether adaptation to spiral motion is preserved in crowding conditions. Logarithmic spirals were used as adapting stimuli. A rotating spiral stimulus (target spiral) was presented, flanked by spirals of the same type, and observers were adapted to its motion. The observers' task was to report the rotational direction of a directionally ambiguous motion (test stimulus) presented afterwards. The directionally ambiguous motion consisted of a pair of spirals flickering in counterphase, which were mirror images of the target spiral. Although observers were not aware of the rotational direction of the target and identified it at chance levels, the direction of rotation reported by the observers during the test phase (motion aftereffect) was contrarotational to the direction of the adapting spiral. Since all contours of the adapting and test stimuli were 90 degrees apart, local motion detectors tuned to the directions of the mirror-image spiral should fail to respond, and therefore not adapt to the adapting spiral. Thus, any motion aftereffect observed should be attributed to adaptation of global motion detectors (ie rotation detectors). Hence, activation of rotation-selective cells is not necessarily correlated with conscious perception.

Adaptation, Physiological↗
PubMed1987

Macromolecular crowding increases binding of DNA polymerase to DNA: an adaptive effect.

Macromolecular crowding extends the range of ionic conditions supporting high DNA polymerase reaction rates. Reactions tested were nick-translation and gap-filling by DNA polymerase I of Escherichia coli, nuclease and polymerase activities of the large fragment of that polymerase, and polymerization by the T4 DNA polymerase. For all of these reactions, high concentrations of nonspecific polymers increased enzymatic activity under otherwise inhibitory conditions resulting from relatively high ionic strength. The primary mechanism of the polymer effect seems to be to increase the binding of polymerase to DNA. We suggest that this effect on protein-DNA complexes is only one example of a general "metabolic buffering" action of crowded solutions on a variety of macromolecular interactions.

Binding Sites↗
PubMed1994

Use of a macromolecular crowding agent to dissect interactions and define functions in transcriptional activation by a DNA-tracking protein: bacteriophage T4 gene 45 protein and late transcription.

We have used a molecular crowding reagent to define functions in the transcriptional activation of bacteriophage T4 late genes. This activation normally requires the three T4 DNA polymerase accessory proteins encoded by T4 genes 44, 62, and 45 (the gp44/62 complex and gp45), an enhancer-like cis-acting site, an RNA polymerase-bound coactivator, and an unobstructed path along the DNA joining the promoter to the enhancer. We show that molecular crowding eliminates the requirement for the gp44/62 complex and for the enhancer, retains the requirement for gp45 and its coactivator, and generates activated promoter complexes with nearly unchanged DNase I footprints. These experiments identify gp45 as the direct activator of transcription, and the gp44/62 complex as the assembly factor for gp45. They suggest that the enhancer serves as the normal, but not invariably essential, entry site for the gp45 DNA-tracking protein.

Adenosine Triphosphate↗
PubMed2006

Membrane-catalyzed nucleotide exchange on DnaA. Effect of surface molecular crowding.

DnaA is the initiator protein for chromosomal replication in bacteria; its activity plays a central role in the timing of the primary initiations within the Escherichia coli cell cycle. A controlled, reversible conversion between the active ATP-DnaA and the inactive ADP forms modulates this activity. In a DNA-dependent manner, bound ATP is hydrolyzed to ADP. Acidic phospholipids with unsaturated fatty acids are capable of reactivating ADP-DnaA by promoting the release of the tightly bound ADP. The nucleotide dissociation kinetics, measured in the present study with the fluorescent derivative 3'-O-(N-methylantraniloyl)-5'-adenosine triphosphate, was dependent on the density of DnaA on the membrane in a cooperative manner: it increased 5-fold with decreased protein density. At all surface densities the nucleotide was completely released, presumably due to protein exchange on the membrane. Distinct temperature dependences and the effect of the crowding agent Ficoll suggest that two functional states of DnaA exist at high and low membrane occupancy, ascribed to local macromolecular crowding on the membrane surface. These novel phenomena are thought to play a major role in the mechanism regulating the initiation of chromosomal replication in bacteria.

Adenosine Triphosphate↗
PubMed1985

Macromolecular crowding accelerates the cohesion of DNA fragments with complementary termini.

Macromolecular crowding increases the rate of nonenzymatic cohesion of the complementary ends of lambda DNA. Both lambda DNA and DNA fragments bearing the cohesive ends of lambda DNA are similarly affected. High concentrations of plasma albumin or Ficoll 70 increase the rate of cohesion by ca. 100-fold whereas high concentrations of polyethylene glycol 8000 cause greater than 2000-fold stimulation in this rate. These results have implications for the mechanism of polymer-stimulated enzymatic ligation of DNA or RNA. In addition, these crowding effects may help to explain the rapid cohesion of lambda DNA observed in vivo. An improved procedure for the recovery of DNA fragments separated by agarose gel electrophoresis is also described.

Bacteriophage lambda↗
PubMed1986

Stabilization of T4 polynucleotide kinase by macromolecular crowding.

T4 polynucleotide kinase rapidly loses activity during its reaction on duplex DNA termini. Addition of high concentrations of nonspecific polymers reverses or prevents this inactivation. In contrast, additions of related materials of lower molecular weight are relatively ineffective in stabilizing the kinase. Such a pattern suggests that the stabilizing effects of polymers on kinase activity are due to macromolecular crowding. An effect of crowding on the known tendency of the kinase to undergo oligomerization reactions is consistent with our observations.

DNA↗
PubMed2005

Structure and stability of DNA quadruplexes under molecular crowding conditions.

A living cell contains generally macromolecules occupying 20-40% of the total volume. To mimic the crowded cellular condition, we prepared solutions including various cosolutes and investigated the influence of the cosolute on the structure and stability of DNA G-quadruplex. As a result, Tetrahymena telomere sequences form well-ordered G-wires in the presence of cosolutes, whereas human telomere sequences remain as compact G-quadruplexes. Since these sequence motif differ by only one base, these results demonstrate that a single base difference in telomere sequences leads to drastically different structures under the molecular crowding conditions. The findings are useful for understanding G-quadruplex structures in cell-like conditions and for design of DNA nanomaterials.

Animals↗
PubMed2003

Contemporary treatment of a crowded Class II division 1 case.

A 12-year-old Caucasian male presented with a severe Class II division 1 incisor relationship on a mild Skeletal II base with an average maxillary-mandibular planes angle and average lower facial height. Crowding was severe in the upper arch and moderate in the lower arch. Treatment was commenced using Twin Block appliances, and followed by extractions in all four quadrants and fixed appliances. This case illustrates the versatility of the Twin Block appliance in the treatment of those cases exhibiting crowding.

Activator Appliances↗
PubMed1990

Crowding depends on contrast.

Previous studies of visual "crowding" in children have been restricted to the use of high contrast optotypes. In this study, visual acuity was measured in a group of 30 normally sighted children using high (96%), medium (11%), and low (4%) contrast Snellen charts and isolated letter cards. The crowding effect was found to be less for low contrast letters than for high contrast letters.

Child↗