Identification of deoxynivalenol- and nivalenol-producing chemotypes of Gibberella zeae by using PCR

Gibberella zeae, a major cause of cereal scab, may be divided into two chemotypes based on production of the trichothecenes deoxynivalenol (DON) and nivalenol (NIV). We cloned and sequenced the gene cluster for trichothecene biosynthesis from each chemotype. G. zeae H-11 is a DON producer isolated from corn, and G. zeae 88-1 is a NIV producer from barley. We sequenced a 23-kb gene cluster from H-11 and a 26-kb cluster from 88-1, along with the unlinked Tri101 genes. Each gene cluster contained 10 Tri gene homologues in the same order and transcriptional directions as those of Fusarium sporotrichioides. Between H-11 and 88-1 all of the Tri homologues except Tri7 were conserved, with identities ranging from 88 to 98% and 82 to 99% at the nucleotide and amino acid levels, respectively. The Tri7 sequences were only 80% identical at the nucleotide level. We aligned the Tri7 genes and found that the Tri7 open reading frame of H-11 carried several mutations and an insertion containing 10 copies of an 11-bp tandem repeat. The Tri7 gene from 88-1 carried neither the repeat nor the mutations. We assayed 100 G. zeae isolates of both chemotypes by PCR amplification with a primer pair derived from the Tri7 gene and could differentiate the chemotypes by polyacrylamide gel electrophoresis. The PCR-based method developed in this study should provide a simple and reliable diagnostic tool for differentiating the two chemotypes of G. zeae.

p53, BCL-2, and Ki-67 expression according to tumor response after concurrent chemoradiotherapy for advanced rectal cancer

BACKGROUND

Concurrent chemoradiotherapy (CCRT) for locally advanced rectal cancer is an important modality for curative resection, but tumors show wide spectrum response. The purpose of this study was to investigate any correlation among related genetic mutations, proliferative index, and tumor response after CCRT.

METHODS

This study included 23 patients with rectal cancer, who were preoperatively staged as at least T3 N1 or T4 (determined by transrectal ultrasonography and MRI). Enrolled patients were given 5-FU 450 mg/m2/day and leucovorin 20 mg/m2/day intravenously for 5 days during weeks 1 and 5 of radiotherapy (45-54 Gy). Surgical resection was performed 4 weeks after completion of the scheduled treatment. Tumor response was classified as CR (complete response), PR (partial response: 50% diminution of tumor volume and downstaging), and NR (no response). Paraffin-embedded tissue obtained before chemoradiotherapy was studied by immunohistochemical staining for p53, BCL-2, and Ki-67. The extent of tumor response was correlated with proliferative activity and was measured by immunostaining Ki-67 proliferative antigen and the expression of p53 and BCL-2 oncoproteins.

RESULTS

All patients were resectable. CR was obtained in 4 patients, PR in 10 patients, and NR in 9 patients. The p53 mutation was noted in 16 patients: NR in 5 patients, PR in 9 patients, and CR in 2 patients (P = .638). BCL-2 expression was noted in 11 patients: NR in 4 patients, PR in 3 patients, and CR in 4 patients (P = .799). The Ki-67 labeling index was NR: 615.4+/-47.2; PR: 663.2+/-20.4; and CR: 765.5+/-58.3 (CR + PR vs. NR, P = .029).

CONCLUSIONS

Immunohistochemical expression of p53 and BCL-2 does not correlate with tumor response after CCRT, but Ki-67 labeling may be a useful parameter for radiosensitive tumors selected for CCRT.

Ginsenoside Rb1 and Rg1 improve spatial learning and increase hippocampal synaptophysin level in mice

We investigated the cognition enhancing effects of ginsenoside Rb1 and Rg1. Mice were trained in a Morris water maze following injection (i.p.) of Rb1 (1 mg/kg) or Rg1 (1 mg/kg) for 4 days. Both Rb1- and Rg1-injected mice showed enhanced spatial learning compared to control animals. The hippocampus, but not the frontal cortex, of treated mice contained higher density of a synaptic marker protein, synaptophysin, compared to control mice. Electrophysiological recordings in hippocampal slices revealed that Rb1 or Rg1 injection did not change the magnitude of paired-pulse facilitation or long-term potentiation. Our results suggest that Rb1 and Rg1 enhance spatial learning ability by increasing hippocampal synaptic density without changing plasticity of individual synapses.

Intravenous 5-fluorouracil versus oral doxifluridine as preoperative concurrent chemoradiation for locally advanced rectal cancer: prospective randomized trials

BACKGROUND

Preoperative radiation treatment with concomitant intravenous infusion of 5-fluorouracil (5-FU) is known to be effective in shrinking and downstaging of tumors. However, chemotherapy has often been limited by its toxicity and poor patient compliance. Oral 5-FU is known to have several advantages over conventional intravenous 5-FU infusion such as lower toxicity and higher quality of life without compromising the efficacy of the treatment. The aim of this study was to compare intravenous 5-FU with oral doxifluridine with respect to tumor response, toxicity and quality of life.

METHODS

Twenty-eight patients with rectal cancer, staged as over T3N1 or T4 by transrectal ultrasonography between July 1997 and December 1998, were included in this study. Intravenous 5-FU (450 mg/m2) and leucovorin (20 mg/m2) were given for five consecutive days during the first and fifth weeks of radiation therapy (50.4 Gy) (n = 14). Oral doxifluridine (700 mg/m2/day) and leucovorin (20 mg/m2) were given daily during radiation treatment (n = 14). Quality of life was scored according to 22 activity items (good, >77; fair, >58; poor, <57). Surgical resection was performed 4 weeks after completion of concurrent chemoradiation treatment. Tumor response was classified into CR (complete remission), PR (partial response; 50% diminution of tumor volume or downstaging ) and NR (no response).

RESULTS

Tumor response was CR 3/14 (21.4%), PR 7/14 (50%) and NR 4/14 (28.6%) in the IV arm versus CR 2/14 (14.2%), PR 6/14 (42.9%) and NR 6/14 (42.9%) in the Oral arm (p = 0.16, 0.23, 0.24), respectively. The quality of life was poor (36.4% versus 33.3%), fair and good (63.6% versus 66.7%) between the IV arm and Oral arm, respectively. Gastrointestinal toxicity was 2/14 (14.3%) in the IV arm versus 5/14 (35.7%) in the Oral arm, respectively. Stomatitis was only observed in the IV arm (1/14, 7.1%). Hematological toxicity was 3/14 (21.4%) in the IV arm versus 4/14 (28.5%) in the Oral arm, respectively. Systemic recurrence during the follow-up periods were 1/14 (7.1%) in the IV arm and 2/14 (14.3%) in the Oral arm, respectively (p = 0.307). One local recurrence was observed in the Oral arm.

CONCLUSION

Even though the results were not entirely reliable owing to the small number of patients enrolled, oral doxifluridine-based chemotherapy as preoperative chemoradiation for advanced rectal cancer did not show any significant advantages over intravenous infusion.

A prospective randomized trial comparing intravenous 5-fluorouracil and oral doxifluridine as postoperative adjuvant treatment for advanced rectal cancer

BACKGROUND

Postoperative adjuvant chemoradiation treatment after curative resection for rectal cancer was needed to reduce recurrence and improve a survival rate. Intravenous 5-fluorouracil (5-FU) and leucovorin has been a mainstay of chemotherapy, but oral 5-FU derivatives have been shown a comparable antitumor activity. Intravenous 5-FU and oral doxifluridine were compared with respect to therapeutic efficacy, drug toxicity, and quality of life.

METHODS

A total of 166 patients were randomized to receive intravenous 5-FU (450 mg/m2/day) or oral doxifluridine (900 mg/m2/day) in combination with leucovorin (20 mg/m2/day) for depth of invasion, nodal status, metastasis (TNM) stage II and III patients between October 1997 and February 1999. Consecutive daily intravenous infusion for 5 days per every month for a total of 12 cycles (IV arm, n = 74) and oral doxifluridine daily for 3 weeks and 1 week rest for a total of 12 cycles (oral arm, n = 92). Drug toxicity and quality of life were observed. Quality of life was scored according to 22 daily activity items (good, > or =71; fair, < 70; poor, < 52).

RESULTS

There was no difference of sex between two groups (IV arm: male/female = 45/29, oral arm: male/female = 59/33). The mean age was 52.3 vs. 59.5, respectively. There was also no difference of TNM stage distribution and type of operation between groups (P>.05). Mean numbers of chemotherapy cycles were 6.5+/-3.7 (IV arm) vs. 7.2+/-4.3 (oral arm), respectively. The rate of recurrence was 9/74 (12.1%) in the IV arm and 6/92 (6.5 %) in the oral arm, respectively (P = .937). Local recurrence was 2/74 (stage III; 2.7%) in the IV arm and 1/92 (stage II; 1.1%) in the oral arm, respectively. Systemic recurrence was 7/74 (stage III; 9.4%) in the IV arm and 5/92 (stage III; 5.4%) in the oral arm, respectively. The most common site of systemic recurrence was the liver. Toxicity profile was as follows: leukopenia (30/74 vs. 17/92) and alopecia (21/74 vs. 13/92) were statistically more common in the IV arm. Diarrhea was more common in the oral arm. Poor quality of life score between two groups was observed at 1 month (23.9% vs. 13%) and 2 months (15.8% vs. 3.7%) after chemotherapy. Good quality of life score was observed at 1 month (19.5% vs. 49%) and 2 months (47% vs. 72%), respectively (P<.05).

CONCLUSIONS

Oral doxifluridine with leucovorin shows a comparable therapeutic efficacy to intravenous 5-FU regimen with high quality of life as postoperative adjuvant therapy. The oral regimen also can be safely given with appropriate toxicity and tolerability.

Molecular organization of mating type loci in heterothallic, homothallic, and asexual Gibberella/Fusarium species

Mating type (MAT) genes were cloned from three members of the Gibberella/Fusarium complex that differ in reproductive mode: heterothallic G. fujikuroi, homothallic G. zeae, and asexual F. oxysporum. The G. fujikuroi MAT locus organization is typical of other heterothallic pyrenomycetes characterized to date; i.e., there are three genes at MAT1-1 and one at MAT1-2. G. zeae has homologues of all four genes encoded by the two G. fujikuroi MAT idiomorphs, tightly linked on the same chromosome, interspersed with sequences unique to G. zeae. Field isolates of F. oxysporum, although asexual, have either the MAT1-1 or the MAT1-2 genes found in sexual species and these genes are highly similar to those of heterothallic G. fujikuroi. RT-PCR analysis proved that the F. oxysporum MAT genes are expressed and that all putative introns found in each of the four MAT genes in G. fujikuroi and F. oxysporum are removed. Apparent failure of F. oxysporum to reproduce sexually could not be attributed to mutations in the MAT genes themselves.

Cholinergic modulation of synaptic transmission and plasticity in entorhinal cortex and hippocampus of the rat

Effects of cholinergic agents on synaptic transmission and plasticity were examined in entorhinal cortex and hippocampus. Bath application of carbachol (0.25-0.75 microM) induced transient depression of field potential responses in all cases tested (24/24 in layer III of medial entorhinal cortex slices and 24/24 in CA1 of hippocampal slices; 11.0+/-1.9% and 7.8+/-2.5%, respectively) and long-lasting potentiation in some cases (4/24 in entorhinal cortex and 12/24 in hippocampus; 33.7+/-3.7% and 32.1+/-9.9%, respectively, in successful cases). Carbachol (0.5 microM) induced transient depression, but not long-lasting potentiation, of N-methyl-D-aspartate receptor-mediated responses in entorhinal cortex. At 5 microM, carbachol induced transient depression only (55. 9+/-4.7% in entorhinal cortex and 41.4+/-2.9% in hippocampus), which was blocked by atropine. Paired-pulse facilitation was not altered during carbachol-induced potentiation but enhanced during carbachol-induced depression. These results suggest that the underlying mechanisms of carbachol-induced depression and potentiation are decreased transmitter release and selective enhancement of non-N-methyl-D-aspartate receptor-mediated responses, respectively. Long-term potentiation could be induced in the presence of 10 microM atropine by theta burst stimulation. The magnitude was significantly lower (15.2+/-5.2%, n=9) compared with control (37.2+/-6.1%, n=8) in entorhinal cortex, however. These results demonstrate similar, but not identical, cholinergic modulation of synaptic transmission and plasticity in entorhinal cortex and hippocampus.

Selective enhancement of non-NMDA receptor-mediated responses following induction of long-term potentiation in entorhinal cortex

The contribution of NMDA receptors to the expression of long-term potentiation (LTP) is controversial. In entorhinal cortex (EC) previous studies reported either that LTP was exclusively expressed through NMDA receptors or that both NMDA and non-NMDA receptors were involved in LTP expression. To reexamine this issue, horizontal entorhinal cortical slices were prepared from adult rats and electrical stimulation was delivered in layer II/III, while field potential recordings were made in layer III. In the standard condition (2.5 mM Mg(++)), LTP was reliably induced by theta burst stimulation, but was blocked by 100 microM D-AP5, an NMDA receptor antagonist. This corroborates previous reports that NMDA receptor activation is required for induction of EC LTP. The field potential response was not affected by D-AP5, but completely blocked by 10 microM CNQX, a non-NMDA receptor antagonist. This indicates that the expression of LTP is mediated by non-NMDA receptors in the standard condition. LTP of NMDA receptor-mediated responses was tested by comparing NMDA responses before and after applying theta burst stimulation in medium containing low magnesium (0.4-1 mM). Theta burst stimulation induced 43.2+/-9.7% increase of non-NMDA responses (i.e., AP5-insensitive fast component) but 5.6+/-9.0% decrease of the NMDA receptor component (AP5-sensitive slow component). These results indicate that activation of NMDA receptors is critical for induction of LTP, but LTP expression is mediated by non-NMDA receptors in EC under these experimental conditions.

Protective effects of asiaticoside derivatives against beta-amyloid neurotoxicity

Asiaticoside (AS) derivatives were tested for potential protective effects against Abeta-induced cell death. Of the 28 AS derivatives tested, asiatic acid (AA), asiaticoside 6 (AS6), and SM2 showed strong inhibition of Abeta-induced death of B103 cells at 1 microM. The three AS derivatives were further tested for their effects on free radical injury and apoptosis. All three AS derivatives reduced H(2)O(2)-induced cell death and lowered intracellular free radical concentration, but AA showed the strongest protection. In contrast, SM2 was the most effective blocker of staurosporine-induced apoptosis. These results suggest that the three AS derivatives block Abeta toxicity by acting through different cellular mechanisms. When applied to hippocampal slices, AA, SM2, and AS6 did not alter n-methyl-D-aspartic acid (NMDA) or non-NMDA receptor-mediated synaptic transmission, paired-pulse facilitation or induction of long-term potentiation in the field CA1. These results indicate that the three AS derivatives do not alter physiological properties of the hippocampus at the concentration that blocks Abeta-induced cell death. Therefore AS6, AA, and SM2 can be regarded as reasonable candidates for a therapeutic Alzheimer's disease drug that protects neurons from Abeta toxicity.

Long-period fiber gratings based on periodic microbends

We demonstrate a new type of high-performance long-period fiber grating based on arc-induced periodic microbends. The fabrication method is simple and does not require special fibers. Flexibility in controlling the filter parameters makes it possible to produce arbitrary filter profiles by use of a simple apodization technique, which is difficult to do with conventional long-period gratings.

Frequency-division-multiplexed polarimetric fiber laser current-sensor array

We demonstrate a novel frequency-domain-multiplexing technique for implementing polarimetric fiber laser current sensors. Each sensor operates at a different polarization-mode beat frequency that is modulated in response to applied electric current. A bank of bandpass filters can be used to separate signals from different sensors. A simple frequency-demodulation technique based on a phase-locked loop is used for signal processing.

Comparative study of transrectal ultrasonography, pelvic computerized tomography, and magnetic resonance imaging in preoperative staging of rectal cancer

PURPOSE

The preoperative assessment of rectal cancer wall invasion and regional lymph node metastasis is essential for the planning of optimal therapy. This study was done to determine the accuracy and clinical usefulness of transrectal ultrasonography, pelvic computed tomography, and magnetic resonance imaging in preoperative staging.

METHODS

A total of 89 patients with rectal cancer were examined with transrectal ultrasonography (n = 89), pelvic computed tomography (n = 69), and magnetic resonance imaging with endorectal coil (n = 73). The results obtained by these diagnostic modalities were compared with the histopathologic staging of specimens.

RESULTS

In staging depth of invasion, the overall accuracy was 81.1 percent (72/89) by transrectal ultrasonography, 65.2 percent (45/ 69) by computed tomography, and 81 percent (59/73) by magnetic resonance imaging. Overstaging was 10 percent (9/89) by transrectal ultrasonography, 17.4 percent (12/69) by computed tomography, and 11 percent (8/73) by magnetic resonance imaging; and understaging was 8 of 89 (8.9 percent) by transrectal ultrasonography, 12 of 69 (17.4 percent) by computed tomography, and 6 of 73 (8 percent) by magnetic resonance imaging. In staging lymph node metastasis, the overall accuracy rate was 54 of 85 (63.5 percent) in transrectal ultrasonography, 39 of 69 (56.5 percent) in computed tomography, and 46 of 73 (63 percent) in magnetic resonance imaging. The sensitivity was 24 of 45 (53.3 percent) in transrectal ultrasonography, 14 of 25 (56 percent) in computed tomography, and 33 of 42 (78.5 percent) in magnetic resonance imaging; and specificity was 30 of 40 (75.0 percent) in transrectal ultrasonography, 25 of 44 (56.8 percent) in computed tomography, and 13 of 31 (41.9 percent) in magnetic resonance imaging. The accuracy in detection of positive lateral pelvic lymph nodes under magnetic resonance imaging (n = 8) was 12.5 percent. The accuracy in detection of posterior vaginal wall invasion was 100 percent in transrectal ultrasonography (n = 7) and 100 percent in magnetic resonance imaging (n = 3), but 28.5 percent in computed tomography (n = 7).

CONCLUSIONS

Both transrectal ultrasonography and magnetic resonance imaging with endorectal coil exhibited similar accuracy and were superior to conventional computed tomography in preoperative assessment of depth of invasion and adjacent organ invasion. Because transrectal ultrasonography is a safer and more cost-effective modality than magnetic resonance imaging, transrectal ultrasonography is an appropriate method for preoperative staging of rectal cancer. Further efforts will be needed to provide a better staging of lymph node involvement.

Evolution of the fungal self-fertile reproductive life style from self-sterile ancestors

In most fungal ascomycetes, mating is controlled by a single locus (MAT). Fungi requiring a partner to mate are heterothallic (self-sterile); those not requiring a partner are homothallic (self-fertile). Structural analyses of MAT sequences from homothallic and heterothallic Cochliobolus species support the hypothesis that heterothallism is ancestral. Homothallic species carry both MAT genes in a single nucleus, usually closely linked or fused, in contrast to heterothallic species, which have alternate MAT genes in different nuclei. The structural organization of MAT from all heterothallic species examined is highly conserved; in contrast, the organization of MAT in each homothallic species is unique. The mechanism of conversion from heterothallism to homothallism is a recombination event between islands of identity in otherwise dissimilar MAT sequences. Expression of a fused MAT gene from a homothallic species confers self-fertility on a MAT-null strain of a heterothallic species, suggesting that MAT alone is sufficient to change reproductive life style.

The translocation-associated tox1 locus of Cochliobolus heterostrophus is two genetic elements on two different chromosomes

Previously, Tox1 was defined as a single genetic element controlling the difference between races of Cochliobolus heterostrophus: race T is highly virulent on T-cytoplasm corn and produces the polyketide T-toxin; race O is weakly virulent and does not produce T-toxin. Here we report that Tox1 is two loci, Tox1A and Tox1B, on two different chromosomes. Evidence for two loci derives from: (1) the appearance of 25% Tox+ progeny in crosses between induced Tox1(-) mutants, one defective at Tox1A, the other at Tox1B; (2) the ability of Tox1A- + Tox1B- heterokaryons to complement for T-toxin production; and (3) electrophoretic karyotypes proving that Tox1(-) mutations are physically located on two different chromosomes. Data showing Tox1 as a single genetic element are reconciled with those proving it is two loci by the fact that Tox1 is inseparably linked to the breakpoints of a reciprocal translocation; the translocation results in a four-armed linkage group. In crosses where the translocation is heterozygous (i.e., race T by race O), all markers linked to the four-armed intersection appear linked to each other; in crosses between induced Tox1(-) mutants, complications due to the translocation are eliminated and the two loci segregate independently.

Interrogation of fiber grating sensor arrays with a wavelength-swept fiber laser

We demonstrate a novel application of a wavelength-swept fiber laser to fiber Bragg grating sensor-array interrogation. The laser provides high signal powers of >3 mW with <0.1-nm spectral resolution over a 28-nm wavelength span. Using time-interval counting, we demonstrate static-dynamic strain measurements with a resolution of 0.47mu? rms at a sampling rate of 250 Hz.

All-fiber acousto-optic tunable notch filter with electronically controllable spectral profile

We demonstrate a novel all-fiber acousto-optic tunable notch filter based on coupling to cladding modes in a single-mode fiber. The device has the advantage of low loss (<0.1 dB) and low polarization dependence. By coupling input light to multiple cladding modes by use of multiple acoustic waves, we achieved an electronically controllable variable spectral profile without a significant coherent cross-talk problem.

All-fiber-optic nonreciprocal modulator

A new all-fiber-optic nonreciprocal device using two acousto-optic frequency shifters is proposed and demonstrated. When the device was operated as an optical isolator, an extinction ratio of 22 dB was obtained. The device's unique modulation capability is also described.

Low-loss all-fiber acousto-optic tunable filter

We report significant advances in the development of simple all-fiber, tunable acousto-optic spectral filters based on null couplers. The performance agrees well with theoretical predictions and is attributed to improved control of the coupler uniformity. Furthermore, using a double-pass arrangement, we demonstrate filter bandwidth reduction and improved sidelobe suppression of -20 dB . The double-pass configuration is also shown to double the frequency shifts that are obtainable from such devices.

Polarization- and frequency-stable fiber laser for magnetic-field sensing

We report a novel polarimetric fiber laser sensor for magnetic-field-current measurement that is stable to variation of temperature and strain because it employs a Faraday rotating mirror. We obtained a sensitivity of 10.24 kHzyA with good linearity and greatly improved the signal-to-noise ratio by reducing the number of laser cavity modes with the help of a saturable absorber.

Nonlinear strain response of two-mode fiber-optic interferometer

Experimental and theoretical investigation of a nonlinear response of a two-mode fiber interferometer to axial strain is described. It is discovered that the nonlinearity dramatically increases as the wavelength approaches the cutoff wavelength of the second-order mode (LP(11)).

Suppression of polarization dependence in a two-mode-fiber acousto-optic device

We present a theoretical and experimental analysis of the polarization dependence of a two-mode-fiber acoustooptic device, taking into account the residual stress in the fiber and the ellipticity of the core. We successfully demonstrate the suppression of the polarization dependence by relieving the residual stress, using thermal annealing.

All-fiber tunable filter and laser based on two-mode fiber

We demonstrate an all-fiber acousto-optic tunable filter based on two-spatial-mode coupling, with improved ruggedness and efficiency, by using a new acoustic-transducer design. We use a rigorous modeling of the flexural acoustic wave to analyze the mode coupling with better accuracy. Using the acousto-optic tunable filter, we demonstrate a novel all-fiber tunable laser with a tuning range of more than 20 nm and a linewidth of 0.2 nm.

Cochlear fistula in chronic otitis media with cholesteatoma

Labyrinthine fistula in chronic otitis media with cholesteatoma most commonly involves the horizontal semicircular canal. We report three cases of cochlear fistula in chronic otitis media with cholesteatoma. All of them had a long history of otorrhea. One patient had total hearing loss of the affected side. The other two patients had conductive hearing loss. Radical mastoidectomy had been done in all cases. Cholesteatoma in the tympanic cavity destroyed the basal turn of the cochlea. These fistulas were sealed with muscle or Gelfoam with streptomycin. We found no fistula in the semicircular canal in any of the three cases. We report three cases of cochlear fistula in chronic otitis media with cholesteatoma, and review the literature.

Structures of the amylopectins of waxy, normal, amylose-extender, and wx:ae genotypes and of the phytoglycogen of maize

Average chain lengths and beta-amylolysis limits have been determined for the waxy and ae/wx genotypes of mature maize starch, and for the amylopectin fractions of normal and amylose-extender starches (prepared by precipitation with concanavalin A), rabbit-liver glycogen, phytoglycogen, and waxy rice starch. All amylopectin samples had similar A:B chain ratios of > 1 and the two glycogens had ratios of < 1. This finding led to average frequencies of substitution of B chains over the whole molecule of > 2 for the amylopectins and < 2 for the glycogens. An equation for the number of tiers for a molecule with various frequencies of substitution of B chains and chain lengths has been used to determine the effect of variation in average frequency of branching and average chain length on structure.