Numbers Of Bursts Research Articles

Short-term impact of a multi-faceted intervention for wheezy infants at risk for asthma

Rationale Urban, low-income children are at increased risk for asthma, likely due to both psychosocial and physical environmental exposures. Methods The Childhood Asthma Prevention Study recruited 177 low-income families of children age 9-24 months with ≥3 wheezing episodes. Half of families were randomly assigned to a year-long nurse home visitor environmental support (ES) intervention focused on reducing allergens and environmental tobacco smoke and improving illness-related caregiving. Assessments at baseline and 12 months addressed caregiver psychological resources, illness management, quality of life, and infant illness symptoms. Infant urine and household dust samples were collected, and medical records were abstracted. Results At year's end, number of homes with cockroach allergen was significantly reduced (p<0.033), and dog allergen tended to be lower (p<0.069) in ES homes. Infants' urinary cotinine was significantly reduced among ES families whose caregivers had fewer psychological resources (p<0.006). Asthma Knowledge and Collaboration with Medical Provider was greater in the ES group (p's<0.04). Reports of children's symptoms did not differ across groups, but caregiver quality of life was greater for ES foreign-born families (p<0.026) and families whose children had low baseline medication levels (p<0.044). Children in the ES group had significantly higher numbers of corticosteroid bursts during the intervention year (p<0.012). Conclusion The nurse home visitor intervention successfully impacted some of the targeted variables assessed, but failed to impact caregivers' symptom reports. Higher numbers of corticosteroid bursts in the ES group may reflect better management for these infant wheezers, possibly leading to less inflammation and fewer symptoms at age 4 and 7 follow-up.

Effects of botulinum toxin on pathophysiology in spasmodic dysphonia.

To determine the mechanism of symptom relief with treatment by botulinum toxin injection in persons with adductor spasmodic dysphonia (ADSD), we evaluated the effects of unilateral thyroarytenoid muscle injections on both injected and noninjected muscles in 10 subjects with ADSD, using electromyography on both sides of the larynx before and after treatment. The subjects' speech symptoms were reduced (p = .005) 2 weeks following injection, when the electromyographic study occurred. Muscle activation levels and the numbers of spasmodic muscle bursts decreased significantly (p < or = .03) postinjection in both the injected and noninjected muscles. The reductions in laryngeal muscle bursts correlated with symptom reduction (r > or = .7) in all muscles. Reductions in laryngeal muscle bursts did not relate to either absolute or normalized levels of muscle activity before or after botulinum toxin injection. The results suggest that changes in the central pathophysiology are responsible for changes in speech symptoms following treatment.

Effects of Cypermethrin on the Electroencephalographic Activity of the Rat: A Model of Chemically Induced Seizures

CONDÉS-LARA, M., A. GRAFF-GUERRERO AND L. VEGA-RIVEROLL. Effects of cypermethrin on the electroencephalographic activity of the rat: A model of chemically induced seizures. NEUROTOXICOL TERATOL 21(3) 293–298, 1999.—Cypermethrin is a potent representative member of the type II pyrethroid insecticides. This pyrethroid is used worldwide and has become a part of our environment. Until the present study, little information about its toxic effects in the central nervous system (CNS) was available. The aim of this study was, then, to determine the effects of repeated exposure to cypermethrin by means of assessing the electroencephalographic (EEG) activity in the rat. Cypermethrin was administered daily in a 300 mg/kg IP dose, below the LD50 value. After daily administration, the EEG activity was recorded and evaluated for 30 min. Paroxysmal epileptic activity appeared after the first and second days of cypermethrin administration. Frequency and numbers of bursts of epileptic activity also increased throughout the days of exposure to cypermethrin. Some of the paroxysmal events were present with behavioral anomalies, such as generalized tonic–clonic seizures. These effects are important because they could be related to the incidence of epileptic activity in humans chronically exposed to cypermethrin.

Effects of four species of interferon-alpha on cultured erythroid progenitors from congenital dyserythropoietic anaemia type I.

The in vitro effects of interferon (IFN)-alpha on erythroid progenitor cells derived from the peripheral blood of five patients with congenital dyserythropoietic anaemia (CDA) type I and seven healthy adults were studied. Ficol-hypaque-separated mononuclear cells were cultured for 14 d in StemGEM-1d medium with 0, 1, 10 and 100 U/ml of recombinant IFN-alpha2a, recombinant IFN-alpha2b, the genetically-engineered hybrid molecule IFN-alpha(1-8) or the laboratory-designed molecule IFN-alpha(consensus). Erythroid bursts and colonies were counted, picked and processed for electron microscopy. In the experiments employing IFN-alpha2a there were no differences in the numbers of erythroid bursts or colonies between four patients with CDA type I and seven healthy adults. All five patients with CDA type I showed the 'Swiss-cheese' ultrastructural abnormality of the heterochromatin in a proportion of the erythroblasts when the progenitor cells were cultured in the absence of added IFN-alpha. A statistically significant reduction in the proportion of erythroblasts showing the 'Swiss-cheese' defect was seen when the erythroid progenitors were cultured in the presence of 0.01-0.5 U/ml IFN-alpha2a (five patients), or 0.1 U/ml of IFN-alpha2b (two patients). In contrast, no reduction was seen in cultures containing 0.1-100 U/ml of either IFN-alpha(1-8) or IFN-alpha(consensus) or 20 microM hydroxyurea (two patients). The partial correction of the 'Swiss-cheese' abnormality by low concentrations of IFN-alpha2a in vitro provides an experimental model with which the mechanisms underlying the haematological response that occurs after the in vivo administration of this species of IFN-alpha may be investigated.

Effects of four species of interferon -&amp; on cultured erythroid progenitors from congenital dyserythropoietic anaemia type I

Summary. The in vitro effects of interferon (IFN)-a on erythroid progenitor cells derived from the peripheral blood of five patients with congenital dyserythropoietic anaemia (CDA) type I and seven healthy adults were studied. Ficolhypaque-separated mononuclear cells were cultured for 14 d in StemGEM-1d medium with 0, 1, 10 and 100 U/ml of recombinant IFN-a2a, recombinant IFN-a2b, the geneticallyengineered hybrid molecule IFN-a1-8 or the laboratorydesigned molecule IFN-aconsensus. Erythroid bursts and colonies were counted, picked and processed for electron microscopy. In the experiments employing IFN-a2a there were no differences in the numbers of erythroid bursts or colonies between four patients with CDA type I and seven healthy adults. All five patients with CDA type I showed the ‘Swiss-cheese’ ultrastructural abnormality of the heterochromatin in a proportion of the erythroblasts when the progenitor cells were cultured in the absence of added IFN-a. A statistically significant reduction in the proportion of erythroblasts showing the ‘Swiss-cheese’ defect was seen when the erythroid progenitors were cultured in the presence of 0·01‐0·5 U/ml IFN-a2a (five patients), or 0·1 U/ml of IFN-a2b (two patients). In contrast, no reduction was seen in cultures containing 0·1‐100 U/ml of either IFN-a1-8 or IFN-aconsensus or 20 mM hydroxyurea (two patients). The partial correction of the ‘Swiss-cheese’ abnormality by low concentrations of IFN-a2a in vitro provides an experimental model with which the mechanisms underlying the haematological response that occurs after the in vivo administration of this species of IFN-a may be investigated.

Stem cell factor induces proliferation and differentiation of fetal progenitor cells in the mouse

We have investigated the kinetics of the amplification of the progenitor cell compartments (CFC) in haemopoietic organs during murine ontogenesis and compared the growth requirements of fetal and adult CFC. Two haemopoietic phases were recognized in the fetal liver (FL): an exponential growth phase, from 11.5 to 15.5 d post conception (p.c.), during which the mean number of nucleated cells and of CFC in the FL increased from 4.9 x 10(5) to 7.0 x 10(7) and from 4.5 x 10(3) to 2.7 x 10(5), respectively, and a recessive phase after 15.5 d p.c., during which the CFC number in the FL gradually decreased, although some CFC were still detectable in the liver after birth. In serum-deprived cultures, FL and adult marrow (AM) CFC had similar responses to GM-CSF, and did not respond to G-CSF or IL-3. In contrast, FL, but not AM, erythroid colonies grew Epo-independently whereas SCF alone induced formation of maximal numbers of erythroid bursts from FL, but not from AM cells. The proliferative and differentiative effect of SCF alone on fetal cells was confirmed in serum-deprived cultures of purified early progenitor cells isolated by cell sorting on the basis of multiple parameters from FL and AM light-density cells. In culture of purified FL cells, SCF alone induced a similar amplification of total cells (maximal amplification at day 12: 800-300-fold) and total CFC (11-38-fold of maximal amplification at day 6) to the combination of SCF plus IL-3 (1300-800-fold amplification of total cells and 31-88-fold amplification of CFC). In contrast, SCF alone allowed only survival of purified AM early progenitor cells. Therefore FL early progenitor cells have an intrinsic higher potential than their adult counterpart to respond to SCF, confirming the potent role of this growth factor in the development of the murine haemopoietic system.

Ovariectomy and Estradiol Affect Postingestive Controls of Sucrose Licking

Hrupka, B. J., G. P. Smith and N. Geary. Ovariectomy and estradiol affect postingestive controls of sucrose licking. Physiol Behav 61(2) 243–247, 1997.—Ovariectomy (OVX) has been shown to increase, and estradiol replacement to decrease, meal size in rats. Because little is known about how estradiol influences meals, we conducted two experiments to examine the effects of OVX and β-estradiol 3-benzoate (EB) replacement on the microstructure of licking behavior. In both experiments, patterns of licking were analyzed in adult female Sprague–Dawley rats during an 0.8 M sucrose test meal. In Experiment 1, meal microstructure was determined preOVX and 10–12 days postOVX. Rate of licking following OVX was not changed during min 1 of the meal, but was significantly faster during min 2–4 of the meal (p < 0.03). The numbers of bursts (runs of licks separated by 250–500 ms) and numbers of clusters (runs of licks separated by > 500 ms) were significantly increased during min 2–4 (p < 0.05). In Experiment 2, OVX rats received EB replacement. Rate of licking after EB replacement was not changed during min 1 of the meal, but was significantly slower during the remainder of the meal (min 2–4, min 5–7, and min 8–10). Burst size, cluster size, and interburst interval were less after EB replacement during min 5–7 of the test meal (all p < 0.05). Because both OVX and EB replacement failed to alter the rate of licking during min 1, estrogen did not appear to alter the palatability of sucrose. OVX and EB replacement did appear to affect a postingestive mechanism(s) that is engaged within 2–4 min of meal onset.

Tests and consequences of disk plus halo models of gamma-ray burst sources

The gamma-ray burst observations made by the Burst and Transient Source Experiment (BATSE) and by previous experiments are still consistent with a combined Galactic disk (or Galactic spiral arm) plus extended Galactic halo model. Testable predictions and consequences of the disk plus halo model are discussed here; tests performed on the expanded BATSE database in the future will constrain the allowed model parameters and may eventually rule out the disk plus halo model. Using examples, it is shown that if the halo has an appropriate edge, BATSE will never detect an anisotropic signal from the halo of the Andromeda galaxy. A prediction of the disk plus halo model is that the fraction of the bursts observed to be in the 'disk' population rises as the detector sensitivity improves. A careful reexamination of the numbers of bursts in the two populations for the pre-BATSE databases could rule out this class of models. Similarly, it is predicted that different satellites will observe different relative numbers of bursts in the two classes for any model in which there are two different spatial distributions of the sources, or for models in which there is one spatial distribution of the sources that is sampled to different depths for the two classes. An important consequence of the disk plus halo model is that for the birthrate of the halo sources to be small compared to the birthrate of the disk sources, it is necessary for the halo sources to release many orders of magnitude more energy over their bursting lifetime than the disk sources. The halo bursts must also be much more luminous than the disk bursts; if this disk-halo model is correct, it is necessary to explain why the disk sources do not produce halo-type bursts.

Implications of the BATSE data for a helocentric origin of gamma-ray bursts

Several possible models have been suggested to explain the observed distribution of gamma-ray bursts: heliocentric distributions such as the Oort cloud, large galactic halos, and cosmological models. We report here on an investigation into the implications of the Burst and Transient Source Experiment (BATSE) gamma-ray burst distribution (Meegan et al. 1992a) data on the possible helocentric origin of gamma-ray bursts. We find no statistically significant anisotropy in the angular distribution of the bursts in a Sun-referenced coordinate system; there is no dipole moment in the direction of the Sun, and no quardrupole moment associated with the ecliptic plane. We have employed direct analytic calculations and Monte Carlo simulations of sources in the Oort cloud to constrain possible helicentric burst distributions. These can produce distributions consistent with the observed angular isotropy, the meal value of V/V(sub max), and the observed C/C(sub min) distribution of BATSE, and provide limits to burst energy of a few times approximately 10(exp 27) ergs. However, the agreement of the heliocentric C/C(sub min) distributions with the BATSE data is attributable to the relatively limited sampling of strong, nearby bursts. These bursts are known from observation to be homogeneously distributed, yet the density of sources in the Oort cloud is not constant in this region. Integral number-intensity distributions from the Oort cloud for larger numbers of bursts cannot reproduce the known homogeneity of the strong bursts without modification to the computed cometary number density and are therefore unlikely explanations of the gamma-ray burst distribution.

Motility and sensation of the rectosigmoid and the rectum in patients with anorectal malformations

Motility of the rectosigmoid and rectum and reservoir function of the rectum after surgery for anorectal malformations were investigated in 32 patients (17 with high type, 6 with intermediate type, and 9 with low type anomaly) aged 5 to 16 years. All 32 patients were examined manometrically as well as with a newly devised myoelectrical method. Manometry showed that the values of maximum anal pressure and anorectal pressure difference in the high type were significantly lower than those in the low type. However, the incidence of contractile activity of the rectosigmoid was not significantly different between these two groups. The threshold sensation pressure and the maximum tolerable pressure in the high type were significantly higher than those in the low type, and the rectal compliance in the high type was significantly lower than that in the low type. Electromyography was recorded at 8 cm and 5 cm from the anal verge. Two types of slow waves were observed, a faster rhythm and a slower rhythm. Their frequency was similar in the three groups. However, the numbers of spike bursts in the high type and intermediate type were significantly higher than those in the low type. These results indicate that in addition to an inadequate anal resting pressure a loss of optimal rectal sensation or rectal reservoir function might be associated with fecal incontinence in the high type and that increased spike bursts might play some role in rectal motility.

Loss Probability of a Burst Arrival Finite Queue with Synchronized Service

We are concerned with a burst arrival single-server queue, where arrivals of cells in a burst are synchronized with a constant service time. The main concern is with the loss probability of cells for the queue with a finite buffer. We analyze an embedded Markov chain at departure instants of cells and get a kind of lumpability for its state space. Based on these results, this paper proposes a computation algorithm for its stationary distribution and the loss probability. Closed formulas are obtained for the first two moments of the numbers of cells and active bursts when the buffer size is infinite.

Synergism Between Erythropoietin and Interleukin-3 in the Induction of Hematopoietic Stem Cell Proliferation and Erythroid Burst Colony Formation

The influence of recombinant erythropoietin (Ep) and interleukin-3 (IL-3) on the proliferation and differentiation of murine hematopoietic stem and progenitor cells was investigated in serum-deprived cultures. The differentiation of progenitor cells, purified by collecting blast cell colonies from spleen cell cultures of 5-fluorouracil-treated mice, was evaluated by scoring the number and type of colonies appearing after eight days in semisolid culture. IL-3 induced the formation of both erythroid and granulocyte-macrophage colonies in a concentration-dependent fashion, the plateau being reached at 300 U/mL. However, concentrations of IL-3 alone that had little or no effect (less than or equal to 10 U/mL) induced maximal numbers of erythroid bursts in the presence of Ep (1.5 IU/mL). In the presence of Ep alone, no colonies were seen. Proliferation of quiescent hematopoietic stem cells, purified by cell sorting and evaluated by spleen colony assay (CFU-S), was investigated by measuring the total cell number and CFU-S content and the DNA histogram at 20 and 48 hours of liquid culture. Almost no cells or CFU-S survived 20 hours of incubation without the addition of IL-3. The presence of either IL-3 (400 U/mL) or the combination of EP and IL-3 (10 U/mL), supported the maintenance of nearly 40% of sorted CFU-S for 48 hours. Approximately 10% of these cells were in the S phase of the cell cycle at 20 hours and an increase in the total cell number per culture, but not in the CFU-S content, was detected at 48 hours. These data indicate that IL-3 exerts a differentiative and proliferative effect on early stem and progenitor cells, which is concentration dependent. At IL-3 concentrations, which had little or no activity alone, Ep acted synergistically to induce both proliferation of stem cells and differentiation of erythroid progenitors.

Synergism between erythropoietin and interleukin-3 in the induction of hematopoietic stem cell proliferation and erythroid burst colony formation

The influence of recombinant erythropoietin (Ep) and interleukin-3 (IL- 3) on the proliferation and differentiation of murine hematopoietic stem and progenitor cells was investigated in serum-deprived cultures. The differentiation of progenitor cells, purified by collecting blast cell colonies from spleen cell cultures of 5-fluorouracil-treated mice, was evaluated by scoring the number and type of colonies appearing after eight days in semisolid culture. IL-3 induced the formation of both erythroid and granulocyte-macrophage colonies in a concentration- dependent fashion, the plateau being reached at 300 U/mL. However, concentrations of IL-3 alone that had little or no effect (less than or equal to 10 U/mL) induced maximal numbers of erythroid bursts in the presence of Ep (1.5 IU/mL). In the presence of Ep alone, no colonies were seen. Proliferation of quiescent hematopoietic stem cells, purified by cell sorting and evaluated by spleen colony assay (CFU-S), was investigated by measuring the total cell number and CFU-S content and the DNA histogram at 20 and 48 hours of liquid culture. Almost no cells or CFU-S survived 20 hours of incubation without the addition of IL-3. The presence of either IL-3 (400 U/mL) or the combination of EP and IL-3 (10 U/mL), supported the maintenance of nearly 40% of sorted CFU-S for 48 hours. Approximately 10% of these cells were in the S phase of the cell cycle at 20 hours and an increase in the total cell number per culture, but not in the CFU-S content, was detected at 48 hours. These data indicate that IL-3 exerts a differentiative and proliferative effect on early stem and progenitor cells, which is concentration dependent. At IL-3 concentrations, which had little or no activity alone, Ep acted synergistically to induce both proliferation of stem cells and differentiation of erythroid progenitors.

Solar cycle variation of long duration 10.7 cm and soft X-ray bursts

Gradual rise-and-fall (GRF) microwave bursts and long duration soft X-ray events (LDEs) are generally accompanied by solar coronal mass ejections (CMEs). We use reports from the Ottawa and Penticton stations to examine the annual variations from 1965 to 1985 of 10.7 cm GRF bursts with total durations of at least 4 hr. The annual numbers of such bursts are well correlated with the quiet-Sun 10.7 cm flux densities. This result is in contrast with the finding of Koomen et al. (1985) that the annual numbers of ≥ 4 hr GOES soft X-ray events are not well correlated with sunspot numbers. We show that the latter result is biased by the large variation of the quiet-Sun X-ray background throughout the solar cycle. Four-hour events are more easily detected in X-ray data than in 10.7 cm data at solar minimum, but, conversely, these events are much more easily detected in 10.7 cm data around solar maximum. About 70% of the most energetic CMEs are associated with ≥ 4 hr X-ray or 10.7 cm bursts. A one-to-one relationship does not exist between CMEs and either LDEs or GRF bursts viewed in full-Sun detectors.

Pure red cell aplasia: response to therapy with anti-thymocyte globulin.

Pure red cell aplasia (PRCA) results from the failure of erythrocyte differentiation and may respond to immunosuppressive therapies. We have treated nine patients with PRCA refractory to steroids and/or cyclophosphamide with anti-thymocyte globulin (ATG). Six patients had normal numbers of erythroid bursts (from erythroid burst-forming units) or erythroid colonies (from erythroid colony-forming units) detectable in vitro, and all responded to therapy with ATG. In vitro studies suggested T-cell inhibition of erythropoiesis in four of these six patients and humorally mediated erythroid suppression in one. In three individuals, virtually no erythroid progenitors were detected in marrow culture. None of these patients responded to ATG. Myelofibrosis, 5q- chromosomal abnormality, or the subsequent development of thrombocytopenia in these individuals suggested that PRCA resulted from an intrinsic stem cell disorder. Our studies demonstrate that ATG is effective therapy for PRCA, and it may be especially useful in children or other patients in whom alkylating agents are not appropriate. We also confirm that erythroid growth in marrow culture predicts those patients who will respond to ATG or other immunosuppressive therapies.

Childhood Erythroleukemia

Marrow hematopoiesis was examined in two infants with erythroleukemia (EL) using cell culture colony assays. At diagnosis, marrow from both yielded normal to increased numbers of granulocytic colonies (CFU-C), erythroid bursts (BFU-E), and mixed colonies (CFU-GEMM), which contrasted sharply with the reduced growth in eight other newly diagnosed patients with acute leukemia. BFU-E proliferation and hemoglobinization proceeded normally in culture and was entirely erythropoietin-dependent. CFU-C colony cellular composition showed normal granulopoiesis in various stages of development. Despite low numbers of morphologically recognizable blasts in the aspirates, they were readily identified in a blast colony assay because of their high plating efficiency and high index of self-renewal on replating. Blast cells in all cultures had myeloblastic morphology, were peroxidase positive, and expressed the granulocytic-specific My-1 antigen. Monosomy 7 was seen in fresh and cultured blast cells but not in lymphocytes, indicating a clonal proliferation. After chemotherapy-induced remission, blast colonies and monosomy 7 could no longer be detected. It appears that the integrity and function of the normal hematopoietic progenitor pool were preserved in these patients with EL. The abnormal myeloblastic proliferation was expressed actively in colony assays and was useful diagnostically in these cases because marrow morphology was nondiagnostic. In these patients, EL seems to be a misnomer since the findings are suggestive of acute myeloblastic leukemia with secondary erythroid and granulocytic hyperplasia.

The Detection of Long Error Bursts During Transmission of Video Signals

In this paper we describe a simple threshold code for monitoring digital communication channels which, with high probability, will detect the presence of an error burst of length at least 70, say, but will ignore shorter bursts. This code has applications to digital systems, such as video-conferencing systems, which have an existing error-correction procedure that can handle small numbers of random errors and bursts of length less than some fixed number, but which are adversely affected by longer bursts.

The Myeloproliferative Sarcoma Virus Causes Transformation of Erythroid Progenitor Cells In Vitro

The myeloproliferative sarcoma virus induces spleen focus formation in vivo and transforms fibroblasts in vitro. We showed in this study that in vitro infection of spleen or bone marrow cells from susceptible mice with the myeloproliferative sarcoma virus leads to the formation of erythroid bursts. Under optimal conditions erythroid bursts formed in the absence of added erythropoietin, but the addition of as little as 0.05 U of erythropoietin per ml to infected cultures resulted in a significant increase in numbers of erythroid bursts and the proportion of hemoglobinized cells. A comparison of the kinetics of burst formation and the size of the induced bursts with those induced with Friend virus suggested that either sarcoma virus such as the myeloproliferative sarcoma virus or the target cells for the two viruses were not the same. Density characterization and heat lability studies indicated that the increased erythroid proliferation in vitro was a virus-induced event, but the possibility that the induced erythroid burst formation is mediated via interaction with a nonerythroid target cell and subsequent release of a soluble factor cannot be ruled out.

The myeloproliferative sarcoma virus causes transformation or erythroid progenitor cells in vitro.

The myeloproliferative sarcoma virus induces spleen focus formation in vivo and transforms fibroblasts in vitro. We showed in this study that in vitro infection of spleen or bone marrow cells from susceptible mice with the myeloproliferative sarcoma virus leads to the formation of erythroid bursts. Under optimal conditions erythroid bursts formed in the absence of added erythropoietin, but the addition of as little as 0.05 U of erythropoietin per ml to infected cultures resulted in a significant increase in numbers of erythroid bursts and the proportion of hemoglobinized cells. A comparison of the kinetics of burst formation and the size of the induced bursts with those induced with Friend virus suggested that either sarcoma virus such as the myeloproliferative sarcoma virus or the target cells for the two viruses were not the same. Density characterization and heat lability studies indicated that the increased erythroid proliferation in vitro was a virus-induced event, but the possibility that the induced erythroid burst formation is mediated via interaction with a nonerythroid target cell and subsequent release of a soluble factor cannot be ruled out.

On the Statistical Nature of Type I Bursts

During noise storms narrow-band, short-lived bursts make up an important part of the activity. Frequently the bursts show different characteristic arrangements in the frequency-time plane (Elgaröy, 1977). In the present investigation the frequency of occurrence of single bursts and sequences of bursts has been determined. The work started out as a search for statistical evidence for the occurrence of echoes of type I bursts. As progress was made, more attention was devoted to the general question of what was the frequency distribution of events containing different numbers of bursts and the conclusions that could be drawn from the observed distribution.