The glass transition time scale and configurational entropy in polymers: an experimental molecular view.

We report direct experimental observation of local conformational dynamics in a polymer chain at the calorimetric glass transition temperature Tg. Variable-temperature two-dimensional (2D) solid-state exchange NMR, at natural abundance, reveals segmental dynamics in pure polyisobutylene (PIB) occurring on a time scale of several seconds over the Tg range observed by DSC (203-208 K). To our knowledge, this is the first direct observation of molecular-level conformer interchange (trans-trans/trans-gauche/gauche-gauche) at the caloric glass transition temperature. Our results provide a chronologically accurate and pedagogically advantageous demonstration of molecular processes during a polymer phase transition, relative to traditional bulk mechanical and calorimetric techniques. More importantly, we use a miscible blend to demonstrate a general strategy for quantitative evaluation of configurational entropy changes via combination of temperature-dependent 2D exchange NMR and Adams-Gibbs theory. Our results on the Tg time scale are directly relevant to fundamental understanding of the Tg length scale, i.e., the dimension of cooperatively rearranging regions.

Risk factors for and impact of online sexual solicitation of youth.

CONTEXT: Health care professionals, educators, and others are increasingly called upon to advise parents and policymakers about risks posed to children by Internet use. However, little scientific information exists on the experiences of children online. OBJECTIVE: To assess the risk factors surrounding online sexual solicitations of youth and distress due to solicitation. DESIGN, SETTING, AND PARTICIPANTS: Telephone survey (August 1999-February 2000) of a random sample of 1501 youth aged 10 through 17 years who were regular Internet users. MAIN OUTCOME MEASURES: Demographic and behavioral characteristics associated with solicitation risk and distress due to solicitation. RESULTS: Nineteen percent of youth who used the Internet regularly were the targets of unwanted sexual solicitation in the last year. Girls (P<.001), older teens (P =.005), troubled youth (P =.004), frequent Internet users (P =.01), chat room participants (P<.001), and those who communicated online with strangers (P<.001) were at greater risk. Twenty-five percent of the solicited youth reported high levels of distress after solicitation incidents. Risk of distress was more common among the younger youth (P =.005), those who received aggressive solicitations (the solicitor attempted or made offline contact) (P =.001), and those who were solicited on a computer away from their home (P =.001). CONCLUSIONS: Many young people who use the Internet encounter unwanted sexual overtures. Health care professionals, educators, and parents should be prepared to educate youth about how to respond to online sexual solicitations, including encouraging youth to disclose and report such encounters and to talk about them.

Police reporting and professional help seeking for child crime victims: a review.

Most crimes with child victims are not reported to police, nor do child victims access other professional victim services, despite evidence that these yield positive outcomes. This article develops a conceptual framework about the barriers to such access: (a) the reluctance to define the crime episodes or their consequences as serious, criminal, harmful, or warranting intervention; (b) the extra authorities, including parents and schools, who mediate between victims and police or services; (c) developmental issues, such as concerns about autonomy; (d) attitudinal and emotional obstacles; and (e) time and expense factors. This article suggests the need for initiatives to stimulate reporting and help seeking, such as more publicity about the seriousness of juvenile victimization, more justice-system involvement with schools, more child and family friendly police services, and an emphasis on attractive outcomes such as justice and empowerment.

Nonsexual assaults to the genitals in the youth population.

OBJECTIVE: To assess the frequency with which youth suffer nonsexual assaults to the genitals and their context and consequences. DESIGN: Telephone survey with follow-up interview 1 year later. SETTING: General population of the United States living in households with telephones. PARTICIPANTS: Random sample of 1042 boys and 958 girls aged 10 through 16 years. RESULTS: A nonsexual assault to the genitals was experienced by 9.2% of the boys and 1.0% of the girls in the year prior to the initial interview and 9.1% of the boys and 2.2% of the girls in the year prior to the follow-up interview. Among the boys, about a quarter of the assaults involved some injury, but only one in 50 needed medical attention. The most common assailants were same-aged peers. The assaults occurred in a variety of contexts including gang attacks, peer fighting, bullying, and some situations in which girls retaliated against the genitals of harassing boys. Boy victims of nonsexual genital assault had significantly higher levels of posttraumatic and depression symptomatology than boys without such assaults. CONCLUSIONS: Nonsexual genital violence needs additional clinical and research attention. Youth should be educated about its possible consequences. Clinicians should ask about nonsexual genital violence when taking a history, particularly with youth who have experienced other kinds of assaults.

Mechanical lithotripsy of large gallstones: correlation with CT characteristics.

The CT characteristics of gallstones were correlated with mechanical forces required to fragment calculi in vitro. Forty-two gallstones > or = 11 mm in largest diameter were subjected to in vitro CT scanning and categorized as isodense, faint, laminated, rimmed, or dense as compared with saline. A mechanical lithotripter, attached to a dynamometer, was utilized simulating in vivo technique to accomplish lithotripsy. Significantly more force was required to fracture CT-dense (p < 0.02) and CT-rimmed (p < 0.05) gallstones than was required to fracture CT-isodense gallstones.

Loss of myeloid differentiation antigens precedes blastic transformation in chronic myelogenous leukemia.

In order to determine whether antigenic patterns alter with disease progression and are thereby suggestive of impending blast crisis in chronic myelogenous leukemia, 50 bone marrow biopsy specimens from 32 patients were examined retrospectively using indirect immunoperoxidase labeling with three monoclonal antibodies that detect myeloid antigens. Monoclonal antibodies PMN13F6, PMN7C3, and PMN8C7 detect human neutrophil antigens that first appear at the myeloblast, promyelocyte, and metamyelocyte stages of differentiation, respectively, and persist throughout later differentiation. Percentages of antigen-positive bone marrow cells during the chronic phase were compared with percentages of antigen-positive cells at blast transformation, and time from bone marrow biopsy until blast crisis was correlated with the percentage of bone marrow cells expressing these antigens. Bone marrow biopsy samples from patients in the chronic phase who continue to remain clinically stable 4 to 106 months after biopsy expressed PMN13F6 antigen on 82% +/- 9% (mean +/- SD) of cells, PMN7C3 antigen on 62% +/- 14% of cells, and PMN8C7 on 68% +/- 14% of cells. Bone marrow biopsy specimens obtained from patients 1 or more years prior to blast transformation expressed PMN13F6 antigen on 81% +/- 12%, PMN7C3 antigen on 71% +/- 16%, and PMN8C7 on 64% +/- 16% of cells. Bone marrow biopsy samples obtained between 2 months and 1 year prior to blast crisis expressed PMN13F6 antigen on 68% +/- 15%, PMN7C3 on 51% +/- 17%, and PMN8C7 antigen on 46% +/- 18% of cells. Bone marrow biopsy specimens taken at the time of blast transformation expressed PMN13F6 antigen on 20% +/- 25%, PMN7C3 antigen on 19% +/- 25%, and PMN8C7 antigen on 13% +/- 25% of cells. The difference between the mean of antigen-positive cells from bone marrow biopsy samples obtained at the time of blast crisis was significant compared with the mean of positive cells from biopsy specimens obtained at all other phases of the disease (P less than .001 for all three antibodies). There was a positive correlation between loss of myeloid antigens and disease progression as determined by simple regression of log time and correlation analysis (PMN13F6, r = .6533, P less than .005; PMN7C8, r = .6304, P less than .005; PMN8C7, r = .5215, P less than .05). There was a negative correlation between percentage of immature cells and time to blastic crisis (r = -.6206, P less than .005).(ABSTRACT TRUNCATED AT 250 WORDS)

Identification of Epstein-Barr nuclear antigen polypeptide in mouse and monkey cells after gene transfer with a cloned 2.9-kilobase-pair subfragment of the genome.

A new antigenic polypeptide was identified in mouse L cells and in monkey COS-1 cells in which Epstein-Barr nuclear antigen (EBNA) was expressed as the result of gene transfer with cloned fragments of Epstein-Barr virus (EBV) DNA. The same-size protein (Mr, approximately equal to 78,000) was seen in stably transformed mouse cells harboring only the BamHI K fragment [approximately equal to 5.2 kilobase pairs (kbp)] or its BamHI/HindIII subfragment, I1f (approximately equal to 2.9 kbp). Thus, the latter DNA fragment is sufficient to code for the protein. In transfected COS cells, a deletion mutant of the I1f fragment (approximately equal to 2.3 kbp) gave rise to a truncated protein (Mr, approximately equal to 52,000), whereas the BamHI K fragment yielded a full-sized Mr 78,000 species. This finding indicates that EBNA is encoded by viral genes. In Burkitt lymphoma lines or in immortalized lymphocytes, variation in the size of the I1f fragment correlated with the apparent molecular weight of the EBNA polypeptide. EBNA is truncated in two Burkitt lymphoma lines, Raji (Mr, 67,000) and P3JHR-1 (Mr, 70,000), which have deletion mutant I1f genes. EBNA in human lymphoid cells bearing a complete I1f fragment as part of the entire EBV genome is the same size (Mr, 78,000) as EBNA found after gene transfer of I1f alone into mouse or monkey cells. Therefore, these expression systems make an authentic EBNA after transfer of the appropriate EBV genes.