bluuebunny/crossref_metadata_2025 huggingface dataset:
Helicobacter pylori Infection in Pediatrics
Authors: Elitsur Yoram , Yahav Jacob
Published: September 2005

The diagnosis of Helicobacter pylori infection continues to challenge practicing physicians around the world. In the last year, several reports from Africa tried to examine the epidemiology of H. pylori infection in nursing babies, while others investigated the association between recurrent abdominal pain symptoms and H. pylori. In the diagnostic arena, attempts were made to improve diagnostic accuracy, mainly by using a new monoclonal version of the stool antigen test, and by applying the urea breath test in smaller children. In the current report, the most important studies on H. pylori infection in children published in the last year are also reviewed.
Bacteria and Mucosal Inflammation of the Gut: Lessons from Helicobacter pylori
Authors: Kuipers Ernst J. , Michetti Pierre
Published: September 2005

The human gastrointestinal tract is colonized by an abundance of bacteria, which are in constant interaction with the epithelial lining usually leading to an intricate balance between tolerance and immunological response. There is ample evidence that the abundant presence of bacteria thus plays a role in the maintenance of human health, as well as in the induction of chronic inflammatory diseases of the gastrointestinal tract. Research in this field is, however, considerably hampered by the abundance of bacterial species, many of which have not even been characterized, and are difficult to culture specifically. These important limitations may to some extent be overcome by recent molecular biologic methods. Furthermore however, the adherent mucosal flora may differ largely from the luminal flora and that in excreta. These characteristics do not pertain to Helicobacter pylori, which generally colonizes the human stomach as a single strain with stable characteristics. Such colonization is stable throughout life, but can be treated. Furthermore, the association with chronic gastritis is very strong. For these reasons, H. pylori serves as an excellent model for the understanding of the processes involved in bacterial colonization and host response including mediation of immunoregulation, and the mechanisms by which this response can lead to disease.
Inflammation, Immunity, and Vaccines for Helicobacter Infection
Authors: Permin Henrik , Andersen Leif P.
Published: September 2005

Pro‐inflammatory cytokines such as IL‐18, IFN‐γ, and IL‐1β play a significant role in the inflammation induced by Helicobacter. During the recent years of H. pylori research, the main focus has been on development of vaccines for therapeutic or prophylactic use against the infection. Both bacterial components of H. pylori as well as engineered vaccines have been tested as well as different forms of administration including systemic and oral/intranasal pathways.
Helicobacter pylori and Gastric Malignancy
Authors: Fischbach Wolfgang , Chan Annie On‐On , Wong Benjamin Chun‐Yu
Published: September 2005

Last year there were a few important clinical data on long‐term prognosis of mucosa‐associated lymphoid tissue (MALT) lymphoma after eradication of Helicobacter pylori. Similarly, there were clinical data to support the role of eradication of H. pylori in the primary prevention of gastric cancer. We understand more about the host susceptibility as well as the pathogenetic mechanisms of the bacteria in the gastric mucosa. This article summarizes the important breakthroughs in H. pylori and gastric malignancies last year.
Pathogenesis of Helicobacter pylori Infection
Authors: Figueiredo Céu , Machado José Carlos , Yamaoka Yoshio
Published: September 2005

As with many infectious diseases, only a fraction of people infected with Helicobacter pylori develop clinical disease, and host genetics, host immune response, and bacterial virulence factors appear to play critical roles. There has been considerable interest in putative bacterial virulence factors and, while several have been identified, it is not clear whether they act independently or in concert. Disease associations have been proposed for the cag pathogenicity island (PAI), vacA, and genes encoding outer membrane proteins (OMPs). Numerous studies published in the last year have provided new insights into the function of these putative virulence factors in gastroduodenal pathogenesis. This article will review the recent novel findings (from April 2004) for the roles of the putative disease‐associated virulence factors as well as their interaction with host.
Helicobacter pylori and Non‐malignant Diseases
Authors: Kupcinskas Limas , Malfertheiner Peter
Published: September 2005

This paper reviews new literature data from March 2004 to April 2005 about the association between Helicobacter pylori and non‐malignant disease of the upper gastrointestinal tract. Eradication of H. pylori is indicated for all patients with non‐malignant diseases associated with this pathogen. However, its effect is variable, ranging from the highest benefit in the cure of peptic ulcer disease to a small benefit in patients with non‐ulcer dyspepsia. Test and treat strategy is still cost‐effective for management of patients with uninvestigated dyspepsia. The only limitations of the strategy are the patient's age and the cost benefit ratio in case of low prevalence of the infection. H. pylori eradication is of value in chronic NSAID users, but is insufficient to prevent NSAID‐related ulcer disease. In developed countries H. pylori eradication does not cause gastro‐esophageal reflux disease (GORD), however, a negative association between H. pylori and GORD does exist, especially in Asia, but the nature of this relationship should be further clarified.
Sinus Node Injury as a Complication of Superior Vena Cava Isolation
Authors: ONG MARY GERTRUDE , TAI CHING‐TAI , LIN YENN‐JIANG , LEE KUN‐TAI , CHANG SHIH‐LIN , CHEN SHIH‐ANN
Published: September 2005

We report a case with SVC ectopy initiating AF; the origin and breakout point of the sinus node was inside the SVC, and the SVC ectopy was conducted through the same path as the sinus node activation to depolarize the right atrium. Injury to the sinus node happened after successful isolation of SVC.
A Feasible Approach for Direct His‐Bundle Pacing Using a New Steerable Catheter to Facilitate Precise Lead Placement
Authors: ZANON FRANCESCO , BARACCA ENRICO , AGGIO SILVIO , PASTORE GIANNI , BOARETTO GRAZIANO , CARDANO PAOLA , MAROTTA TIZIANA , RIGATELLI GIANLUCA , GALASSO MARIAPAOLA , CARRARO MAURO , ZONZIN PIETRO
Published: September 2005

Introduction: Much clinical evidence has shown that right ventricular (RV) apical pacing is detrimental to left ventricular function. Preservation of the use of the His‐Purkinje (H‐P) system may be ideal in heart block that is restricted to the AV node, but may be of no benefit when H‐P disease exists.

Aim: To investigate the feasibility of direct His‐bundle pacing (DHBP) using a new system consisting of a steerable catheter and a new 4.1 F screw‐in lead.

Method: Between May and December 2004, 26 patients (19 male, mean age: 77 ± 5 years) with a standard pacemaker (PM) indication and preserved His‐bundle conduction were enrolled and DHBP was attempted.

Results: DHBP was achieved in 24 patients (92%); two patients were paced in the His area, but the paced QRS morphology and duration were different from the native QRS. The mean time for lead positioning was 19 ± 17 minutes, the mean fluoroscopy time was 11 ± 8 minutes, and the total procedure time (skin‐to‐skin including positioning of a quadripolar diagnostic catheter for His recording) was 75 ± 18 minutes. In DHBP pacing, the acute pacing threshold was 2.3 ± 1.0 V at a pulse duration of 0.5 msec, and the sensed potentials were 2.9 ± 2.0 mV. At a 3‐month follow‐up examination, the same QRS duration and morphology recorded on implantation were observed in all patients. The pacing threshold was 2.8 ± 1.4 V, and sensed potentials were 2.5 ± 1.8 mV; the sensing configuration was changed from bipolar to unipolar in 6 patients to resolve undersensing issues. No major complications were observed.

Conclusions: This feasibility study shows that DHBP can be accomplished with a new system consisting of a steerable catheter and an active fixation lead in 92% of the patients in whom it was attempted.
Correlation of Symptoms to ECG Diagnosis Following Atrial Fibrillation Ablation
Authors: KLEMM HANNO U. , VENTURA RODOLFO , ROSTOCK THOMAS , BRANDSTRUP BENEDIKT , RISIUS TIM , MEINERTZ THOMAS , WILLEMS STEPHAN
Published: September 2005

Introduction: Currently, definition of success following atrial fibrillation (AF) ablation is commonly based on the lack of symptoms. The purpose of this study was to evaluate the correlation between symptoms and the underlying rhythm after AF ablation.

Methods and Results: Eighty consecutive patients (pts) were treated for paroxysmal episodes of AF by segmental ostial ablation of all pulmonary veins and right atrial isthmus ablation. For 6 months pts transmitted transtelephonic (T‐) ECG recordings in combination with comments daily or in the event of symptoms. Eligible comments were classified as: (1) asymptomatic, (2) symptomatic. Analysis was performed at 1‐month intervals, defining an acute (first month) and chronic period (second to sixth month) after ablation. Overall 6,835 T‐ECGs were analyzed. Of these 5,437 (79.5%) showed sinus rhythm (SR) and 1,398 (20.5%) showed AF. Pts in SR reported symptoms for 593 (10.9%) episodes, whereas 4,844 (89.1%) episodes were asymptomatic. During AF, 646 (46.2%) episodes were associated with symptoms, and 752 (53.8%) episodes remained asymptomatic. Exclusively asymptomatic were 7 (8.8%) pts. In 30 (52.6%) of 57 pts with AF, arrhythmic events were confined to the acute phase. Of the remaining 27 pts 14 (52%) reported an improvement, 12 (44%) the same, and 1 (4%) worsened symptoms after 3 months. A significant change (P < 0.01) toward more asymptomatic episodes from the acute (43.5%) to the chronic (57.5 ± 4.5%) period was evident.

Conclusion: Assessment of success after AF ablation cannot be based on the absence of symptoms due to a high prevalence of asymptomatic episodes.
Interface reaction at dental implants inserted in condensed bone
Authors: Büchter André , Kleinheinz Johannes , Wiesmann Hans Peter , Jayaranan Mythili , Joos Ulrich , Meyer Ulrich
Published: September 2005

Purpose: The influence of the osteotome technique on the interface reaction of cylinder implants (SLA, ITI®) was compared with the interface reaction of conventional implant insertion in an animal model.

Material and methods: A total of 64 implants were placed in the cranial and caudal tibia of 8 Göttinger minipigs. The implant site was prepared either by a conventional technique with drills (control group A) or by the osteotome technique (experimental group B). Bone tissue responses were evaluated by histomorphometry, fluorescence microscopy and scanning electron microscopy after 7 and 28 days of osseointegration.

Results: The average initial (7 days) bone‐to‐implant contact ratio was not statistically significantly different for the osteotome technique (35.88±2.94%) than for the control group (43.78±3.39%, P<0.095). After 28 days, the bone‐to‐implant contact ratio became statistically significantly higher when implants were inserted by conventional preparation (44.81±3.07% (group B), 63.47±4.87% (group A), P=0.003). Whereas fluorescence and immunhistologic examination revealed new bone formation with osteocalcin deposition directly at the implant surface in both groups, the extent of direct bone/implant contact was enhanced in conventionally prepared implant sites. SEM analysis confirmed an intimate bone to implant bond without fibrous tissue formation in places of direct contact at an ultrastructured level.

Conclusion: Implant placement in conventionally prepared implantation sites is accompanied by an improved interface formation at an early stage of implantation.
Bone–implant contact at calcium phosphate‐coated and porous titanium oxide (TiUnite™)‐modified oral implants
Authors: Xiropaidis Andreas V. , Qahash Mohammed , Lim Won Hee , Shanaman Richard H. , Rohrer Michael D. , Wikesjö Ulf M. E. , Hall Jan
Published: September 2005

Background: Calcium phosphate (CP)‐coated implants are usually referred to as having osteoconductive properties, whereas titanium implants with a native oxide layer are considered less osteoconductive. Often smooth titanium oxides (TOs) are compared to relatively rough CP structures. The objective of this study was to evaluate osteoconduction by comparing bone–implant contact at a relatively smooth, highly crystalline CP coating with a structured, porous TO (TiUnite™)‐modified surface.

Material and methods: Ten adult Hound Labrador mongrel dogs were used. Four titanium implants (Nobel Biocare) with CP‐coated (2) or TO‐modified (2) surfaces were installed 12 weeks following mandibular premolar and molar teeth extraction. The implants were alternated within and between jaw quadrants in consecutive animals. Mucosal flaps were advanced and sutured leaving the implants in a submerged position. The animals were injected with fluorescent bone labels at 3 and 4 weeks postsurgery, and pre‐euthanasia to monitor progress of bone formation. The animals were euthanized at 8 weeks postsurgery and block biopsies were prepared for histologic and histometric analysis.

Results: There were no remarkable differences in bone formation and apparent bone–implant contact comparing the TO‐modified and CP‐coated surfaces. However, the measured average bone–implant contact was 71% and 57% (P=0.027) for TO‐modified and CP‐coated implants, respectively.

Conclusions: We conclude that the TO surface exhibits osteoconductive properties exceeding that of the CP surface. One or several of the chemical and physical properties of the TO surface may result in the remarkable bone formation along its surface. This study indicated that crystallinity and/or chemistry may be important.
Sinus floor elevation applied tissue‐engineered bone
Authors: Ohya Morimichi , Yamada Yoichi , Ozawa Ryotaro , Ito Kenji , Takahashi Makoto , Ueda Minoru
Published: September 2005

Abstract: In the present study, we compared bone regeneration ability in sinus floor elevation between a tissue engineering method using mesenchymal stem cells (MSCs) and platelet‐rich plasma (PRP), and a promising new method using particulate cancellous bone and marrow (PCBM) and PRP. Bilateral sinus floor elevation procedures were performed in 18 adult Japanese white rabbits. MSCs/PRP or PCBM/PRP complexes were grafted to each maxillary sinus in the same rabbits. The MSCs were isolated from rabbit iliac crest marrow, and PRP was obtained from peripheral blood. PCBM were collected from the rabbit iliac crest and mixed with PRP. The animals were sacrificed at 2, 4, and 8 weeks after transplantation, and the bone formation ability of each implant was evaluated histologically and histometrically. According to the histological observations, both sites (MSCs/PRP and PCBM/PRP) showed well newly formed bone and neovascularization at 2 and 4 weeks. However, at 8 weeks, the lamellar bone was observed to be occupied by fatty marrow in large areas in both sites. There was no significant difference in bone volume or augmented height between MSCs/PRP and PCBM/PRP groups each week, but there were significant differences in bone volume and augmented height between 2 and 8 weeks in PCBM/PRP or MSCs/PRP groups and in bone volume between 4 and 8 weeks in the PCBM/PRP group (P<0.05). These results suggest that the MSCs/PRP complex may well be used for bone regeneration in sinus floor elevation, compared with the PCBM/PRP complex.
Influence of alcohol and tobacco habits on peri‐implant marginal bone loss: a prospective study
Authors: Galindo‐Moreno Pablo , Fauri Mounir , Ávila‐Ortiz Gustavo , Fernández‐Barbero Juan Emilio , Cabrera‐León Andrés , Sánchez‐Fernández Elena
Published: September 2005

Abstract: A prospective clinical study was conducted to explore the possible link between peri‐implant bone loss and the widespread habits of tobacco smoking and alcohol consumption. One hundred and eighty‐five patients who received 514 implants were followed up for 3 years. Peri‐implant marginal bone loss was evaluated by digital panoramic radiography and image analysis techniques. Multivariate analysis showed that peri‐implant marginal bone loss was significantly related to a daily consumption of >10 g of alcohol, tobacco use and increased plaque levels and gingival inflammation. The present results indicate that daily alcohol consumption and tobacco use may have a negative influence on predictable long‐term implant treatment outcomes, producing peri‐implant bone loss and compromising restorative treatment with implant‐supported prostheses.
Accuracy of navigation‐guided socket drilling before implant installation compared to the conventional free‐hand method in a synthetic edentulous lower jaw model
Authors: Hoffmann Jürgen , Westendorff Carsten , Gomez‐Roman German , Reinert Siegmar
Published: September 2005

Abstract: In this study, the three‐dimensional (3D) accuracy of navigation‐guided (NG) socket drilling before implant installation was compared to the conventional free‐hand (CF) method in a synthetic edentulous lower jaw model. The drillings were performed by two surgeons with different years of working experience. The inter‐individual outcome was assessed. NG drillings were performed using an optical computerized tomography (CT)‐based navigation system. CF drillings were performed using a surgical template. The coordinates of the drilled sockets were determined on the basis of CT scans. A total of n=224 drillings was evaluated. Inter‐individual differences in terms of the surgeons' years of work experience were without statistical significance. The mean deviation of the CF drilled sockets (n=112) on the vestibulo‐oral and mesio‐distal direction was 11.2±5.6° (range: 4.1–25.3°). With respect to the NG drilled sockets (n=112), the mean deviation was 4.2±1.8° (range: 2.3–11.5). The mean distance to the mandibular canal was 1.1±0.6 mm (range: 0.1–2.3 mm) for CF‐drilled sockets and 0.7±0.5 mm (range: 0.1–1.8 mm) for NG drilled sockets. The differences between the two methods were highly significant (P<0.01). A potential benefit from image‐data‐based navigation in implant surgery is discussed against the background of cost‐effectiveness.
A Distance‐Drawdown Aquifer Test Method for Aquifers with Areal Anisotropy
Authors: Mutch Robert D
Published: September 2005

A new distance‐drawdown method for aquifers with anisotropy on the horizontal plane is presented. The method uses scalar transformation to convert to an equivalent, isotropic medium, thus permitting application of the Cooper‐Jacob Method. The method is applicable to cases where at least one ellipse of equal drawdown can be delineated but can also be applied where no ellipse can be discerned from the data. In the latter case, a least‐squares regression approach can be employed to estimate the orientation and magnitude of the anisotropy. The regression R2 value provides a quantitative assessment of the degree to which the drawdown data are indicative of a systematic areal anisotropy in the aquifer or whether the data simply reflect natural aquifer heterogeneity. In addition to confined aquifers, this methodology, like the Cooper‐Jacob Method, is also applicable to unconfined aquifers either before the onset of delayed drainage or following the completion of delayed drainage provided that the u value meets the recommended criterion.
Effects of Acer platanoides invasion on understory plant communities and tree regeneration in the northern Rocky Mountains
Authors: Reinhart Kurt O. , Greene Erick , Callaway Ragan M.
Published: September 2005

Quantitative studies are necessary to determine whether invasive plant species displace natives and reduce local biodiversity, or if they increase local biodiversity. Here we describe the effects of invasion by Norway maple Acer platanoides on riparian plant communities and tree regeneration at two different scales (individual tree vs stand scales) in western Montana, USA, using both descriptive and experimental approaches. The three stands differed in community composition with the stand most dominated by A. platanoides invasion being more compositionally homogenous, and less species rich (−67%), species even (−40%), and diverse (−75%) than the two other stands. This sharp decrease in community richness and diversity of the highly invaded stand, relative to the other stands, corresponded with a 28‐fold increase in A. platanoides seedlings and saplings. The dramatic difference between stand 1 vs 2 and 3 suggests that A. platanoides invasion is associated with a dramatic change in community composition and local loss of species diversity; however, other unaccounted for differences between stands may be the cause. These whole‐stand correlations were corroborated by community patterns under individual A. platanoides trees in a stand with intermediate levels of patchy invasion. At the scale of individual A. platanoides canopies within a matrix of native trees, diversity and richness of species beneath solitary A. platanoides trees declined as the size of the trees increased. These decreases in native community properties corresponded with an increase in the density of A. platanoides seedlings. The effect of A. platanoides at the stand scale was more dramatic than at the individual canopy scale; however, at this smaller scale we only collected data from the stand with intermediate levels of invasion and not from the stand with high levels of invasion. Transplant experiments with tree seedlings demonstrated that A. platanoides seedlings performed better when grown beneath conspecific canopies than under natives, but Populus and Pinus seedlings performed better when grown beneath Populus canopies, the dominant native. Our results indicate that A. platanoides trees suppress most native species, including the regeneration of the natural canopy dominants, but facilitate conspecifics in their understories.
Effect of grazing on plant patterns in arid ecosystems of Patagonian Monte
Authors: Bisigato Alejandro J. , Bertiller Mónica B. , Ares Jorge O. , Pazos Gustavo E.
Published: September 2005

Our objective was to assess the relationship between the spatial patterning of perennial grasses (total, grazed, and non‐grazed) and shrub patches in rangelands under different grazing pressures of the Patagonian Monte. We selected three grazed paddocks with the usual stocking rate for the area, where previous studies showed that a piosphere formation is common. At each paddock, we analysed the grain of heterogeneity at sites located at two distances from the single watering point (near, far), using high‐resolution aerial photographs. At these sites, we also assessed in the field the density, size, cover, and spatial patterning of grazed and non‐grazed perennial grasses and shrub patches. The grain of heterogeneity of shrub patches was coarser in sites near the watering point than in those distant from it, as a consequence of the increase in size of both, bare soil and shrub patches. Field sampling showed that a coarse grain of heterogeneity relative to fine‐grained sites resulted from changes in species composition, increased bare soil areas and reduced perennial grass cover. In coarse‐grained sites, lower perennial grass cover resulted from lower density and/or smaller size of grass bunches than in fine‐grained sites. We did not find significant differences among sites in the proportion of perennial grazed grasses. Since the density and cover of perennial grasses was higher in fine‐ than in coarse‐grained sites, we suggested that fine‐grained sites are more important as feeding stations than coarse‐grained sites. The consequences of this differential use could lead to degradation of fine‐grained sites and to higher homogeneity in spatial plant structure and floristic composition within paddocks with respect to the condition observed at present, increasing the size of the highly degraded zone within the piosphere. At the patch level, we found that at about one third of the sampled transects, both total and non‐grazed perennial grasses were spatially aggregated with shrub patches. However, in most transects grazed perennial grasses were indifferently distributed in relation with shrub patches, showing that grazers display high selectivity of foraging sites at macro level (i.e. high and low grazing pressure sites at the paddock level), but random occupancy of vegetation units (randomness in the distribution of grazed perennial grasses at the patch level). The intensity of the positive association between non‐grazed grasses and shrub patches was higher in fine‐grained than in coarse‐grained sites and may be attributed to higher protection against herbivores associated to denser shrub patches in fine‐ relative to coarse‐grained sites. We concluded that a feedback exists between the spatial distribution of species preferred by grazers and the spatial patterning of use of these species.
Aggregated distribution of resources creates competition refuges for rainforest dung beetles
Authors: Horgan Finbarr G.
Published: September 2005

This study examines the effects of resource distribution on colonisation, intra‐ and interspecific aggregation, and the occurrence of low‐density, competition refuges for tropical dung beetles. In field experiments from central Peru, using dung pats (resource patches) of different volumes, the numbers of interacting species and total beetle biomass at individual pats increased with increasing pat volume. In two of three separate experiments (including an experiment that also varied patch density), this represented a decrease in the biomass of beetles per unit volume (biomass‐density) at larger patches. The numbers of interacting tunneller species and tunneller biomass‐density were also related to the distance between pats (patch density) in one of two experiments with constant numbers of pats. Closely positioned pats had generally fewer interacting species and a lower biomass‐density of beetles. For the most abundant Dichotomius species, interspecific associations increased as distances increased between dung pats. The numbers of interacting species and biomass‐density declined linearly under the combined effects of increasing patch density and local patch abundance in 25 m2 plots. In experimentally placed grids with large numbers of pats, colonisation of pats at the edge of the grids was generally higher than at the centre of the grids for tunnellers and Eurysternus spp. but not for ball rollers; however, at least tunnellers did not readjust to avoid patches with high densities of competitors. These results indicate that an aggregated distribution of dung and natural variability in patch size contribute to species coexistence by creating low‐density refuges for weaker competitors.
Egg laying by a butterfly on a fragmented host plant: a multi‐level approach
Authors: Rabasa Sonia G. , Gutiérrez David , Escudero Adrián
Published: September 2005

Egg placement by herbivorous insects is an important step in their interaction with their host plants, and is the result of processes operating at different spatial and temporal scales. Although several studies have examined egg‐placement patterns at different scales, this has rarely been achieved simultaneously using a multi‐scale hierarchical approach. We studied egg placement in a rare European butterfly,Iolana iolas, whose larvae specifically feed on seeds of plants of the genusColutea,using a hierarchical approach and Generalised Linear Mixed Modelling. The study was carried out in 2002 and 2003 in a ca 60 km2area in southern Madrid province, Spain, where the host plant,Colutea hispanica, has a highly fragmented distribution. We monitored in detail 132 plants in 24 patches and estimated the abundance of butterflies over the whole reproductive period ofC. hispanica. We measured phenological, morphological and landscape variables potentially affecting egg‐placement at three hierarchical levels: fruit, plant and host plant patch. Using egg presence–absence on mature fruits as the response variable, we found that eggs were more likely to be laid on fruits aged 1–2 weeks at the middle of the flowering period (fruit level), on large plants with a small number of shoots at the base (plant level), and in well connected host plant patches (patch level). Our results suggest that egg‐placement is a process determined by factors operating at different levels: fruit, plant and host plant patch. Because egg‐placement studies are often made with spatially correlated data, neglecting their intrinsic hierarchical nature could lead to equivocal conclusions.
Adaptive advantages of myrmecochory: the predator‐avoidance hypothesis tested over a wide geographic range
Authors: Manzaneda Antonio J. , Fedriani Jose M. , Rey Pedro J.
Published: September 2005

The predator‐avoidance hypothesis states that once released from the parent plant, myrmecochorous seeds are rapidly taken by ants to their nests, where they are protected from predators. Previous studies conducted to test this hypothesis have frequently neglected two major aspects necessary for its verification: 1) the influence of processes acting after the seed release and 2) the spatial evenness of such processes. Thus, large‐scale variations in the mechanisms acting beyond seed release, and possibly influencing seed escape from predators, remain poorly documented. Here, we present the results of a post‐dispersal seed‐removal experiment on the myrmecochorous herb Helleborus foetidus, aimed at verifing the predator‐avoidance hypothesis by considering two key post‐release aspects of seed fate: seed destination (dispersed or nondispersed) and seed burial (buried or not buried). Experiments were performed in four different regions in the Iberian Peninsula. After three days of exposure of seeds to the main predator (fieldmice Apodemus sylvaticus), ca 30% of the seeds were removed. Seed destination affected the proportion of seeds escaping predation, but the sign, magnitude and statistical significance of the effect varied among the geographical regions. In the southern region (Cazorla), seeds dispersed in ant nests or intermediate destinations suffered scarcely any predation, but seeds under reproductive‐age plants experienced losses ca 50%. Conversely, in the northern region (Caurel), seeds in nests suffered significantly greater losses than seeds under plants or intermediate destinations, suggesting that nests were especially unsafe destinations. Seed burial had a strong impact on seed escape from predators, and its effect was highly consistent among geographical regions. In view of the consistency of its effect at different spatial scales, seed burial was a more general mechanism for predation avoidance than seed relocation to ant nests, which was habitat‐ and/or ant‐species‐dependent. Our results thus only partially support the predator‐avoidance hypothesis for the evolution of myrmecochory.
On the Physics of Drag Racing
Authors: Fox Geoffrey T.
Published: September 2005

The sport of drag racing can be very usefully examined in an introductory mechanics course. The concepts of energy, momentum, acceleration, velocity, torque, and power are all involved in the analysis of the problem. Many students find the problem to be very contemporary and close to their own experience. High interest among the students usually results in increased understanding of the physical principles involved.
On the Equation of State for Gases
Authors: Tykodi R. J. , Hummel Edward P.
Published: September 2005

The general thermodynamic structure of equations of state is discussed. It is pointed out that empirical equations of state always involve a double set of assumptions. A recipe for producing thermodynamically consistent empirical equations of state is presented and is illustrated in the step-by-step production of yet another equation of state.
An Experiment to Measure Boltzmann's Constant
Authors: Horne Michael , Farago Peter , Oliver John
Published: September 2005

We describe a simplification of Jean Perrin's classic experiment to determine Boltzmann's constant from the sedimentation equilibrium of colloidal suspensions. Perrin's complicated procedure for preparing suitable colloidal particles is avoided by using commercially available plastic spheres of specified diameter and density. The experiment is suitable for either an introductory or advanced laboratory.
The Measurement of e/k in the Introductory Physics Laboratory
Authors: Inman Fred W. , Miller Carl E.
Published: September 2005

The ratio of electronic charge to Boltzmann's constant can be easily determined by measuring the short-circuit collector current versus the emitter-base voltage characteristics of a silicon transistor connected in the common-base mode. The incorporation of this experiment in the introductory physics laboratory is recommended.
Gas Supported Pucks
Authors: Jones H. W. , Hunt M.
Published: September 2005

The performance of carbon dioxide-supported pucks which have been used in the freshman laboratories of the physics department of the University of Calgary for several years is described. The theory of W. M. Whitney regarding air supported pucks is commented on and is compared with that of Deuker and Wojtech and their experimental measurements. The principle of floating stability is commented on and a criterion for a stable design given.
Physics Taught as a Liberal Art
Authors: Nedelsky Leo
Published: September 2005

This article is a slightly edited part of the xeroxed syllabus used by the students of a one-quarter, non-calculus, no-laboratory course, “Aims and Rules in Physics.” The students range from humanities freshmen to physics seniors. The course analyzes a few discoveries and inventions of prerelativistic physics in the light of physicists' and philosophers' views on science and reality. These views are included in the syllabus in the form of short quotations. No philosophical erudition is required of the instructor.
Teaching Exponential Growth and Decay: Examples from Medicine
Authors: Hobbie Russell K.
Published: September 2005

A treatment of exponential growth and decay is sketched which does not require a previous course in calculus. Rate of change is introduced by considering compound interest and is determined graphically by using semilog paper. Examples of exponential growth and decay are given which will interest premedical students. These include bacterial growth, sterilization, survival in certain chronic diseases, clearance, and drug absorption.
Monte Carlo Calculations as an Aid in Teaching Statistical Mechanics
Authors: Landau D. P. , Alben R.
Published: September 2005

A simple Monte Carlo sampling method is used to illustrate the principles of statistical mechanics as applied to a simple magnetic system. The concepts of ensembles, statistical averages, and responses are clarified particularly with respect to the role of statistical fluctuations. The basic properties of magnetic phase transitions are also demonstrated using small systems of interacting moments.
Physics of the Quark Model
Authors: Young Robert D.
Published: September 2005

The basic ideas of the quark model are explained in a manner that should make the presentation clear to students who have completed a course in undergraduate quantum mechanics. Some simple calculations which can be performed by advanced undergraduate students with appropriate guidance from an instructor are presented.
A Soluble Self-Consistent Nuclear Model
Authors: de Llano M.
Published: September 2005

The self-consistent, independent-particle Hartree equations for N fermions interacting with a separable (in configuration space) two-body potential are solved exactly in one and three dimensions. The exclusion principle is accounted for by allowing only one particle per orbital state. The possibility of only a finite number of particles being bound self-consistently, for given two-body force parameters, is studied and the effect of introducing the observed (in real nuclei) approximate constancy with particle number of particle density and common well depth is also considered.
The Complete Asymptotic Expansion of the Continuum Schrödinger Wave Function
Authors: Lieber M.
Published: September 2005

A complete asymptotic expansion, in inverse powers of the distance, for the scattered wave function solution to Schrödinger's equation with a short-range potential is derived by two simple arguments. The result is identical to a more rigorous calculation by Buslaev. The difference between the asymptotic series and the exact wave function vanishes at infinity faster than any negative power of the distance. Explicit formulas for the coefficients are derived and their physical significance discussed. The application to the uniqueness theorem for the Schrödinger equation is also discussed.
Elimination of Retarded Functions from Two-Body Classical Relativistic Electrodynamics
Authors: Kasher John C.
Published: September 2005

Interaction problems in classical relativistic electro-dynamics are frustratingly difficult to solve, since the differential equation of motion involves functions of both the present and retarded times. In this paper the author eliminates the retarded functions from the equation of motion for the two-body problem in which two equal masses with opposite charges that are equal in magnitude are released from rest and allowed to fall into one another. In the final form of the equation of motion only the present time, the present position, and derivatives of the present position with respect to the present time appear—in other words, it is an equation with one unknown and the present time only. To accomplish this simplification of the equation of motion, the author employs the Lorentz condition, ∇·A+δΦ/cδt=0, and the expression E=−∇Φ−δA/cδt to obtain a partial differential equation in the retarded separation distance R that can be solved. When the resulting relationships are substituted into the Lorentz force equation it contains only functions of the present time.
Solutions of Kronig-Penney Models by the T-Matrix Method
Authors: Titus William J.
Published: September 2005

The energies and wavefunctions of an electron in a one-dimensional crystal are obtained for two Kronig-Penney models directly from the T matrix. The problems serve as good examples of the T-matrix method and indicate the usefulness of this approach in studying the behavior of electrons in crystals.
Numerical Solution to Transient Heat Flow Problems
Authors: Kobiske Ronald A. , Hock Jeffrey L.
Published: September 2005

We first consider the partial differential equation that governs one-dimensional heat flow in a homogeneous medium. This equation is reduced to a difference equation, and the problem of difference equation stability and convergence is discussed and examples of the breakdown of each are given. Next, the above analysis is extended to a three-dimensional space with spherical symmetry. Several interesting problems are programmed and the solutions are displayed in graphical form. The accuracy of the numerical difference technique is checked by comparison with exact Fourier series solutions. The paper is mainly intended for beginning students of physics and engineering, and also for college teachers who have not had a formal course in numerical solutions of partial differential equations.
Photon Dosimetry by Luminescence Methods
Authors: Raeside D. E.
Published: September 2005

A brief, elementary introduction to the dosimetry of photon radiation fields using thermoluminescent and radio-photoluminescent dosimeters is presented. This presentation should be useful for both teachers and students desiring to learn more about the important subject of health physics.
Participatory Lecture Demonstration with an 83-Ton Bar Electromagnet
Authors: Reines F. , Ballard R.
Published: September 2005

An 83-ton bar electromagnet constructed as part of a cosmic ray research facility on the University of California at Irvine campus has been used in a participatory lecture demonstration to show the characteristics of the magneto-static field and the Faraday-Henry induction law.
Irreversible Processes
Authors: Sillescu Hans
Published: September 2005

The model of a linear Rayleigh gas is used to demonstrate some basic features of irreversible processes. The macroscopic aspects of the model provide an introduction to the conceptions of friction, relaxation, complex susceptibility, and energy dissipation. Fluctuations are discussed on the basis of a Langevin equation for the model that is derived starting from elementary collision dynamics. The relation between observable fluctuations and molecular dynamics is elucidated in terms of time correlation functions for the model and for real systems. Examples are given including the transport of matter, electricity, momentum, and energy as well as dielectric, magnetic, and chemical relaxation.
Solution of a Faraday's Law Problem Including a Nonlinear Term
Authors: White John J.
Published: September 2005

It is argued that undergraduates planning to become applied physicists should be exposed to homework problems involving realistic complications. The example presented is a simple electromechanical system that exhibits nonlinear effects if the resistance of two rails cannot be neglected. The method of perturbations is used to obtain the first-order correction to the linearized system, thus illustrating a possible approach for dealing with realistic models.
The Forced Harmonic Oscillator and the Zero-Phonon Transition of the Mössbauer Effect
Authors: Ninio F.
Published: September 2005

The Heisenberg picture solution of the forced harmonic oscillator is specialized to the case when the force is an impulse, and the result is used to illustrate very simply the zero-phonon feature of the Mössbauer effect.
A Simple Illustration of the Uncertainty Relation in Hadronic Collisions
Authors: Amand J. St. , Uritam R. A.
Published: September 2005

In a student's first encounter with “nonintuitive” concepts of quantum theory, such as the uncertainty relation, he is eager to see physical examples and applications of these principles. We present here a simple illustration of the uncertainty principle in the currently active area of high energy hadronic collisions; the discussion is fully comprehensible at the undergraduate level.
Project Laboratory on the Growth of Pyroelectric Crystals for Infrared Detector Applications
Authors: Duley W. W. , Finnigan P. J.
Published: September 2005

An experiment involving the growth of triglycine sulfate (TGS) single crystals and their use as infrared detectors is discussed. Suitable crystals can be grown from solution in 13 days. The properties of the pyroelectric detector are examined and the response of crystals grown by the present technique to chopped CO2 laser radiation has been evaluated.
A Self-Paced Approach to Graduate Quantum Mechanics
Authors: Barnhill M. V.
Published: September 2005

A graduate course in quantum mechanics has been taught to groups of 10–12 students by a self-pacing method. The core of the system is a comprehensive set of problems, with credit being given for the problem only after it has been correctly worked. Scores on an examination indicate that the course is successful in teaching core material at a high mastery level.
The Atmosphere and the Ocean: A Field Study Course
Authors: Donnelly Denis P.
Published: September 2005

A beginning course, carried out entirely off campus, which dealt with physical properties of the atmosphere and the ocean is described. Experiments and measurements included determination of the radius of the Earth, beach profiles, surface currents, sediment transport, and wave properties. The emphasis of the course was not on the results of the measurements; rather it was on a general approach, a method of observing, questioning, and seeking answers.
Quantum Theory of a Square Well Plus Delta Function Potential
Authors: Gettys W. Edward
Published: September 2005

The s-wave Schrödinger equation is solved for a square well potential with an attractive delta function at the well edge. This potential provides a number of soluble illustrations of the techniques of quantum mechanics. The bound state eigenvalue problem is solved as is the scattering problem for the cross section. The potential is capable of producing a sharp low energy resonance. The resonances are discussed using both R-matrix and S-matrix methods. Numerical examples are presented.
Ellipsometric Measurements on Thermally Evaporated Thin Films
Authors: Hilton John W. , Hilton Wallace A.
Published: September 2005

An undergraduate experiment for the optics laboratory or for an independent study project is described. Thermally evaporated thin aluminum films are formed in a vacuum of about 10−5 Torr. Two methods of film thickness measurements are presented. Ellipsometric measurements of the principal angle of incidence φ̄ and the principal azimuth ψ̄ are made on aluminum films of various thicknesses.
Resource Letter EMAA-1: Educational Materials in Astronomy and Astrophysics
Authors: Berendzen Richard , DeVorkin David
Published: September 2005

Prepared at the request of the AAPT Committee on Research Letters. This is one of a series of Resource Letters on different topics intended to guide college physicists to some of the literature and other teaching aids that may help them improve course contents in specified fields of physics. No Resource Letter is meant to be exhaustive and complete; in time there may be more than one letter on some of the main subjects of interest. Comments and suggestions concerning the content and arrangement of letters as well as suggestions for future topics will be welcomed. Please send such communications to Prof. Arthur Quinton, Chairman, Resource Letter Committee, Department of Physics, University of Massachusetts, Amherst, Massachusetts 01002 (current address until Fall of 1973: Prof. Arthur Quinton, Department of Nuclear Physics, Australian National University, Box 4 P.O., Canberra ACT, Australia 2600).
An Interactive Instruction Session in Ray Tracing
Authors: Finn Edward J.
Published: September 2005

A set of interactive programs have been produced which assist a student to self-test himself for an understanding of ray-tracing techniques. The three programs discussed are concerned with plane mirror reflections and the images formed.
Continuous Quantitative Measurements on a Linear Air Track
Authors: Vogel Eric
Published: September 2005

Described in this article is an apparatus, attachable to a linear air track, for recording the continuous motion of one or two carts over several transits of the track. The records thus produced allow one to determine the motion characteristics of the cart(s), such as velocity change during transit versus time, to an accuracy of about one percent. Also discussed are various experiments, such as acceleration due to gravity, force versus acceleration, simple harmonic motion, and collisions which have been performed using this apparatus, as well as an analysis of the basic accuracy of the data.
Introduction to Chirp Concepts with a Cheap Chirp Radar
Authors: Bloch S. C.
Published: September 2005

The elements of pulse compression of a chirp in a dispersive delay are reviewed and chirp and pulse modes are contrasted. A simple microwave Doppler-shift apparatus is modified info a chirp system to permit distance measurement in a laboratory experiment that is rich in fundamental concepts of physical parameters which are related by the Fourier transform, and which involve the convergence of ideas from several disciplines.
Microwave Experiments for an Advanced Laboratory
Authors: Elmore W. C.
Published: September 2005

Four advanced undergraduate laboratory experiments using X-band microwaves are described. The experiments include microwave measurements, electron spin resonance, the cyclotron resonance of electrons, and the electron density in a plasma. Considerable experimental detail is supplied for the latter two.
The Relation “Closer Than” in Minkowski Space
Authors: Williams Gareth
Published: September 2005

A relation “closer than,” having physical interpretation, is defined on Minkowski space. The group of automorphisms of the relation is that generated by the Poincaré group and dilatations.