Showing papers by "University of Nebraska–Lincoln published in 2000"

Framing Processes and Social Movements: An Overview and Assessment

Abstract: ■ Abstract The recent proliferation of scholarship on collective action frames and framing processes in relation to social movements indicates that framing processes have come to be regarded, alongside resource mobilization and political opportunity processes, as a central dynamic in understanding the character and course of social movements. This review examines the analytic utility of the framing literature for un- derstanding social movement dynamics. We first review how collective action frames have been conceptualized, including their characteristic and variable features. We then examine the literature related to framing dynamics and processes. Next we review the literature regarding various contextual factors that constrain and facilitate framing processes. We conclude with an elaboration of the consequences of framing processes for other movement processes and outcomes. We seek throughout to provide clarifi- cation of the linkages between framing concepts/processes and other conceptual and theoretical formulations relevant to social movements, such as schemas and ideology.

Conditioned place preference: What does it add to our preclinical understanding of drug reward?

Abstract: Rationale: Among the various experimental protocols that have been used to measure drug reward in laboratory animals, conditioned place preference (CPP) has been one of the most popular. However, a number of controversial issues have surrounded the use of this experimental protocol. Objective: The present review provides a theoretical overview of some critical issues relevant to CPP. The advantages and limitations of CPP are also covered. Results: Based on modern and traditional theoretical formulations of Pavlovian conditioning, CPP appears to reflect a preference for a context due to the contiguous association between the context and a drug stimulus. Within this theoretical framework, it seems clear that CPP measures a learning process that is fundamentally distinct from drug self-administration. The main advantages of CPP are that it: (1) tests animals in a drug-free state; (2) is sensitive to both reward and aversion; (3) allows for simultaneous determination of CPP and locomotor activity; (4) is adaptable to a variety of species; (5) typically yields dose-effect curves that are monophasic rather than biphasic; and (6) has utility in probing the neural circuits involved in drug reward. The main limitations of CPP are that it: (1) is subject to interpretation based on the notion of novelty seeking; (2) is cumbersome for providing the graded dose-effect curves needed for answering some pharmacological questions; (3) is difficult to interpret when animals prefer one context prior to drug conditioning; and (4) lacks face validity as an experimental protocol of drug reward in humans. Conclusion: Despite some limitations, CPP provides unique information about the rewarding effect of contextual cues associated with a drug stimulus.

Fluvial responses to climate and sea‐level change: a review and look forward

Abstract: Summary Fluvial landforms and deposits provide one of the most readily studied Quaternary continental records, and alluvial strata represent an important component in most ancient continental interior and continental margin successions. Moreover, studies of the long-term dynamics of fluvial systems and their responses to external or ‘allogenic' controls, can play important roles in research concerning both global change and sequence-stratigraphy, as well as in studies of the dynamic interactions between tectonic activity and surface processes. These themes were energized in the final decades of the twentieth century, and may become increasingly important in the first decades of this millennium. This review paper provides a historical perspective on the development of ideas in the fields of geomorphology/Quaternary geology vs. sedimentary geology, and then summarizes key processes that operate to produce alluvial stratigraphic records over time-scales of 103−106 years. Of particular interest are changes in discharge regimes, sediment supply and sediment storage en route from source terrains to sedimentary basins, as well as changes in sea-level and the concept of accommodation. Late Quaternary stratigraphic records from the Loire (France), Mississippi (USA), Colorado (Texas, USA) and Rhine–Meuse (The Netherlands) Rivers are used to illustrate the influences of climate change on continental interior rivers, as well as the influence of interacting climate and sea-level change on continental margin systems. The paper concludes with a look forward to a bright future for studies of fluvial response to climate and sea-level change. At present, empirical field-based research on fluvial response to climate and sea-level change lags behind: (a) the global change community's understanding of the magnitude and frequency of climate and sea-level change; (b) the sequence-stratigraphic community's desire to interpret climate and, especially, sea-level change as forcing mechanisms; and (c) the modelling community's ability to generate numerical and physical models of surface processes and their stratigraphic results. A major challenge for the future is to catch up, which will require the development of more detailed and sophisticated Quaternary stratigraphic, sedimentological and geochronological frameworks in a variety of continental interior and continental margin settings. There is a particular need for studies that seek to document fluvial responses to allogenic forcing over both shorter (102−103 years) and longer (104−106 years) time-scales than has commonly been the case to date, as well as in larger river systems, from source to sink. Studies of Quaternary systems in depositional basin settings are especially critical because they can provide realistic analogues for interpretation of the pre-Quaternary rock record.

Sampling: Design and Analysis

Abstract: In his seminal book, Shewhart (1931) makes no demand on the distribution of the characteristic to be plotted on a control chart. How then can we explain the idea that normality is, if not required, at least highly desirable? I believe that it has come about through the many statistical studies of control-chart behavior. If one is to study how a control chart behaves, it is necessary to relate it to some distribution. The obvious choice is the normal distribution because of its ubiquity as a satisfactory model. This is bolstered by the existence of the Central Limit Theorem.

Prioritizing test cases for regression testing

Abstract: Test case prioritization techniques schedule test cases in an order that increases their effectiveness in meeting some performance goal. One performance goal, rate of fault detection, is a measure of how quickly faults are detected within the testing process; an improved rate of fault detection can provide faster feedback on the system under test, and let software engineers begin locating and correcting faults earlier than might otherwise be possible. In previous work, we reported the results of studies that showed that prioritization techniques can significantly improve rate of fault detection. Those studies, however, raised several additional questions: (1) can prioritization techniques be effective when aimed at specific modified versions; (2) what tradeoffs exist between fine granularity and coarse granularity prioritization techniques; (3) can the incorporation of measures of fault proneness into prioritization techniques improve their effectiveness? This paper reports the results of new experiments addressing these questions.

Long‐term dynamics of pine and hardwood litter in contrasting environments: toward a global model of decomposition

Abstract: We analysed data on mass loss after five years of decomposition in the field from both fine root and leaf litters from two highly contrasting trees, Drypetes glattca, a tropical hardwood tree from Puerto Rico, and pine species from North America as part of the Long-Term lntersite Decomposition Experiment (LIDEn. L1DET is a reciprocal litter­ bag study involving the transplanting of litter from 27 species across 28 sites in North and Central America reflecting a wide variety of natural and managed ecosystems and climates, from Arctic tundra to tropical rainforest. After 5 years, estimated k-values ranged from 0.032 to 3.734, lengths of Phase I (to 20% mass remaining) from 0.49 to 47.92 years, and fractional mass remaining from 0 to 0.81. Pine litter decomposed more slowly than Drypetes litter, supporting the notion of strong control of substrate quality over decomposition rates. Climate exerted strong and consistent effects on decomposi­ tion. Neither mean annual temperature or precipitation alone explained the global pat­ tern of decomposition; variables including both moisture availability and temperature (i.e. actual evapotranspiration and DEFAC from the CENTURY model) were generally more robust than single variables. Across the LIDET range, decomposition of fine roots exhibited a QI0 of 2 and was more predictable than that of leaves, which had a higher QI0 and greater variability. Roots generally decomposed more slowly than leaves, regardless of genus, but the ratio of above- to belowground decomposition rates differed sharply across ecosystem types. Finally, Drypetes litter decomposed much more rapidly than pine litter in 'broad leaved habitats' than in 'conifer habitats', evidence for a 'home-field advantage' for this litter. These results collectively suggest that relatively simple models can predict decomposition based on litter quality and regional climate, but that ecosystem-specific problems may add complications.

Social disorganization outside the metropolis: an analysis of rural youth violence*

Abstract: In order to extend the study of community social disorganization and crime beyond its exclusive focus on large urban centers, we present an analysis of structural correlates of arrest rates for juvenile violence in 264 nonmetropolitan counties of four states. Findings support the generality of social disorganization theory: Juvenile violence was associated with rates of residential instability, family disruption, and ethnic heterogeneity. Though rates of poverty were not related to juvenile violence, this is also in accord with social disorganization theory because, unlike urban settings, poverty was negatively related to residential instability. Rates of juvenile violence varied markedly with population size through a curvilinear relationship in which counties with the smallest juvenile populations had exceptionally low arrest rates. Analyses used negative binomial regression (a variation of Poisson regression) because the small number of arrests in many counties meant that arrest rates would be ill suited to least-squares regression.

The Differential Relations of Parent and Peer Attachment to Adolescent Adjustment

Abstract: Whether or not close emotional relationships with parents and peers serve similar functions for adolescent adjustment is an issue of increasing interest. The present study was designed to examine the relations between parent and peer attachment and adolescent adjustment. Eighty-nine adolescents (M age = 16.1 years, SD = 1.8 years) completed self-report measures of parent and peer attachment, sympathy, academic efficacy, aggression, anxiety, and depression. Adolescents were divided into four groups on the basis of their parent and peer attachment scores: those high on both, those low on both, those high on peer but low on parent attachment, and those high on parent but low on peer attachment. Discriminant function analyses revealed that the groups differed only along one dimension, suggesting that parent and peer attachment served similar functions in terms of the adjustment indices measured. Adolescents high on both peer and parent attachment were the best adjusted (i.e., least aggressive and depressed, most sympathetic) and those low on both were the least well adjusted. Furthermore, those high on peer but low on parent attachment were better adjusted than those high on parent but low on peer attachment, suggesting that peer attachment may be relatively more influential on adolescent adjustment than parent attachment.

Older Consumers' Disposition of Special Possessions

Abstract: This article explores precipitating events, emotions, and decisions associated with older consumers’ disposition of special possessions. Findings are based on analyses of semistructured interviews with 80 older consumers, complemented by depth interviews with seven informants. Cherished possessions and their disposition play a significant role in older consumers’ reminiscence and life review. Concerns about disposition of special possessions involve strong and ambivalent emotions. Older consumers voice concern over avoiding intrafamilial conflict, reducing uncertainty, and exercising control over the future life of special possessions. We emphasize the storied nature of the meanings consumers attach to their cherished possessions and the way in which these storied meanings are bundled with life review and disposition concerns. Many older consumers attempt to control meanings transferred with cherished possessions. They seek to pass on personal and familial legacies, achieve symbolic immortality, insure a ...

School Discipline at a Crossroads: From Zero Tolerance to Early Response:

Abstract: Dramatic incidents of school violence have thrust school discipline to the forefront of public consciousness. Despite a dramatic increase in the use of zero tolerance procedures and policies, there is little evidence demonstrating that these procedures have increased school safety or improved student behavior. Moreover, a punitive disciplinary climate may make any attempt to include more students with behavioral problems a cause for conflict between general and special educators. A preventive, early response disciplinary model increases the range of effective options for addressing violence and disruption across both general and special education. Ultimately, the effectiveness of any disciplinary system may be judged by the extent to which it teaches students to solve interpersonal and intrapersonal problems without resorting to disruption or violence.

Oxalic Acid, a Pathogenicity Factor for Sclerotinia sclerotiorum , Suppresses the Oxidative Burst of the Host Plant

Abstract: Effective pathogenesis by the fungus Sclerotinia sclerotiorum requires the secretion of oxalic acid. Studies were conducted to determine whether oxalate aids pathogen compatibility by modulating the oxidative burst of the host plant. Inoculation of tobacco leaves with an oxalate-deficient nonpathogenic mutant of S. sclerotiorum induced measurable oxidant biosynthesis, but inoculation with an oxalate-secreting strain did not. Oxalate inhibited production of H2O2 in tobacco and soybean cultured cell lines with a median inhibitory concentration of ∼4 to 5 mM, a concentration less than that measured in preparations of the virulent fungus. Several observations also indicate that the inhibitory effects of oxalate are largely independent of both its acidity and its affinity for Ca2+. These and other data demonstrate that oxalate may inhibit a signaling step positioned upstream of oxidase assembly/activation but downstream of Ca2+ fluxes into the plant cell cytosol.

Method for volumetric tissue ablation

Abstract: A volumetric tissue ablation apparatus includes a probe having a plurality of wires journaled through a catheter with a proximal end connected to the active terminal of a generator and a distal end projecting from a distal end of the catheter. The probe wire distal ends are arranged in an array with the distal ends located generally radially and uniformly spaced-apart from the catheter distal end. A conductor connected to the return terminal of the generator is located relative to the probe wire array to form a closed electrical circuit through tissue to be ablated. Preferably, the probe wire array includes 10 wires, each formed in an arch from the catheter distal end. The conductor can be either a conventional ground plate upon which the tissue is supported, or a conductor wire extending through the probe and electrically insulated from the probe wires.

The Quantitatively Important Relationship between Homocysteine Metabolism and Glutathione Synthesis by the Transsulfuration Pathway and Its Regulation by Redox Changes

Abstract: Homocysteine is a key junction metabolite in methionine metabolism. It suffers two major metabolic fates: transmethylation catalyzed by methionine synthase or betaine homocysteine methyl transferase and transsulfuration catalyzed by cystathionine beta-synthase leading to cystathionine. The latter is subsequently converted to cysteine, a precursor of glutathione. Studies with purified mammalian methionine synthase and cystathionine beta-synthase have revealed the oxidative sensitivity of both junction enzymes, suggesting the hypothesis that redox regulation of this pathway may be physiologically significant. This hypothesis has been tested in a human hepatoma cell line in culture in which the flux of homocysteine through transsulfuration under normoxic and oxidative conditions has been examined. Addition of 100 microM H(2)O(2) or tertiary butyl hydroperoxide increased cystathionine production 1.6- and 2.1-fold from 82 +/- 7 micromol h(-)(1) (L of cells)(-)(1) to 136 +/- 15 and 172 +/- 23 micromol h(-)(1) (L of cells)(-)(1), respectively. The increase in homocysteine flux through the transsulfuration pathway exhibited a linear dose dependence on the concentrations of both oxidants (50-200 microM H(2)O(2) and 10-200 microM tertiary butyl hydroperoxide). Furthermore, our results reveal that approximately half of the intracellular glutathione pool in human liver cells is derived from homocysteine via the transsulfuration pathway. The redox sensitivity of the transsulfuration pathway can be rationalized as an autocorrective response that leads to an increased level of glutathione synthesis in cells challenged by oxidative stress. In summary, this study demonstrates the importance of the homocysteine-dependent transsulfuration pathway in the maintenance of the intracellular glutathione pool, and the regulation of this pathway under oxidative stress conditions. Aberrations in this pathway could compromise the redox buffering capacity of cells, which may in turn be related to the pathophysiology of the different homocysteine-related diseases.

Fermentation of fructooligosaccharides by lactic acid bacteria and bifidobacteria.

Abstract: Lactic acid bacteria and bifidobacteria were screened of their ability to ferment fructooligosaccharides (FOS) on MRS agar. Of 28 strains of lactic acid bacteria and bifidobacteria examined, 12 of 16 Lactobacillus strains and 7 of 8 Bifidobacterium strains fermented FOS. Only strains that gave a positive reaction by the agar method reached high cell densities in broth containing FOS.

Environmental Ethical Decision Making in the U.S. Metal-Finishing Industry

Abstract: We investigated the individual and contextual influences shaping the environmental ethical decision intentions of a sample of managers in the U.S. metal-finishing industry in this study. Ajzen's (1991) theory of planned behavior and Jones's (1991) moral intensity construct grounded our theoretical framework. Findings revealed that the magnitude of consequences, a dimension of moral intensity, moderated the relationships between each of five antecedents—attitudes, subjective norms, and three perceived behavioral control factors (self-efficacy, financial cost, and ethical climate)—and managers' environmental ethical decision intentions. We then developed implications for theory and practice in environmental ethical decision making.

Identification of regional soil quality factors and indicators : I. Central and Southern High Plains

Abstract: Appropriate indicators for assessing soil quality on a regional scale using the National Resource Inventory (NRI) are unknown. Our objectives were to (i) identify soil quality factors present at a regional scale, (ii) determine which factors vary significantly with land use, and (iii) select soil attributes within these factors that can be used as soil quality indicators for regional-scale assessment. Ascalon (fine-loamy, mixed, superactive, mesic Aridic Argiustoll) and Amarillo (fine-loamy, mixed, thermic Aridic Paleustalf) soils were sampled from a statistically representative subset of NRI sample points within the Central and Southern High Plains Major Land Resource Areas (MLRA) and analyzed for 20 soil attributes. Factor analysis was used to identify soil quality factors, and discriminant analysis was used to identify the factors and indicators most sensitive to land use within each MLRA. In the Central High Plains, five soil quality factors were identified, with the organic matter and color factors varying significantly with land use. Discriminant analysis selected total organic C (TOC) and total N as the most sensitive indicators of soil quality at a regional scale. In the Southern High Plains, six factors were identified, with water stable aggregate (WSA) content, TOC, and soil salinity varying significantly with land use. Discriminant analysis selected TOC and WSA content as the most sensitive indicators of soil quality in the Southern High Plains. Total organic C was the only indicator that consistently showed significant differences between land uses in both regions.

The Legacy of Early Attachments

Abstract: The impact of early close relationships on psychological development is one of the enduring questions of developmental psychology that is addressed by attachment theory and research. This essay evaluates what has been learned, and offers ideas for future research, by examining the origins of continuity and change in the security of attachment early in life, and its prediction of later behavior. The discussion evaluates research on the impact of changing family circumstances and quality of care on changes in attachment security, and offers new hypotheses for future study. Considering the representations (or internal working models) associated with attachment security as developing representations, the discussion proposes that (1) attachment security may be developmentally most insuential when the working models with which it is associated have sufÞciently matured to insuence other emerging features of psychosocial functioning; (2) changes in attachment security are more likely during periods of representational advance; and (3) parentÐchild discourse and other relational insuences shape these developing representations after infancy. Finally, other features of early parentÐchild relationships that develop concurrently with attachment security, including negotiating consict and establishing cooperation, also must be considered in understanding the legacy of early attachments.

Economic Circumstances and Family Outcomes: A Review of the 1990s

Abstract: This review documents the economic context within which American families lived in the 1990s. Despite nearly full employment and growing income and wealth for many Americans, problem areas included persistent racial gaps in economic well-being, growing inequality, and declining wages for young men. Women showed stronger income growth than men in the decade, and 2-earner households became increasingly associated with advantage. We review the consequences of these trends and of economic well-being generally on 4 dimensions of family outcomes: family formation, divorce, marital quality, and child well-being. Despite hypotheses suggesting that women's earnings might have different effects on family outcomes than men's earnings, generally the review supports the expectation that both men's and women's economic advantage is associated with more marriage, less divorce, more marital happiness, and greater child well-being. Important issues regarding measurement, reciprocal relations between family structure and economic well-being, and race and gender effects remain unresolved.

The Ecology of School Psychology: Examining and Changing Our Paradigm for the 21st Century.

Abstract: A conceptual model (paradigm) for school psychology is presented based upon ecological and contextual considerations that frame the practice, training, and research agendas of the field. We argue t...

Mother–Child Discourse, Attachment Security, Shared Positive Affect, and Early Conscience Development

Abstract: The separate literatures on parental discipline, maternal discourse about emotion, and autobiographical memory support the idea that parent-child discourse in the context of a supportive relationship plays a role in a child's early conscience development, and this study was designed to examine this issue. Forty-two preschool children and their mothers took part in a 45-min structured laboratory session, and at their homes, mothers completed the Attachment Q-Set. As part of the laboratory session, each mother was asked to discuss with her child one incident that occurred within the last week in which her child behaved well and one in which her child misbehaved. These conversations were transcribed verbatim and coded for maternal references to feelings, rules, consequences of the child's actions, and moral evaluatives. Each child also took part in a behavioral measure of internalization and several compliance tasks, and mothers completed a maternal report of the child's early conscience development. Consistent with attachment theory, attachment security predicted maternal and child references to feelings and moral evaluatives. Attachment security, shared positive affect between the mother and child, and maternal references to feelings and moral evaluatives also predicted specific aspects of early conscience development.

Human Rights in International Relations

Abstract: This fourth edition of David P Forsythe's successful textbook provides an authoritative and timely analysis of the place of human rights in an age of upheaval in international politics Human rights standards are examined at the global, regional and national levels, with separate chapters on transnational corporations and advocacy groups Completely updated and revised, the fourth edition takes account of new sources and recent scholarship, as well as recent events, such as the Syrian war, the rise of ISIS, refugee flows, South Sudan crises, and the resurgence of nationalism A new chapter has been added on the media and human rights, covering both traditional and social media Examining attempts to protect human rights by various actors, such as the United Nations, the European Union, transnational corporations, and the media, the book stresses that the open-ended fate of universal human rights depends on human agency in this context Containing further reading suggestions and discussion questions, this textbook is a vital resource for courses on human rights in an international context

Chemical and biological trends during lake evolution in recently deglaciated terrain.

Abstract: As newly formed landscapes evolve, physical and biological changes occur that are collectively known as primary succession. Although succession is a fundamental concept in ecology, it is poorly understood in the context of aquatic environments. The prevailing view is that lakes become more enriched in nutrients as they age, leading to increased biological production. Here we report the opposite pattern of lake development, observed from the water chemistry of lakes that formed at various times within the past 10,000 years during glacial retreat at Glacier Bay, Alaska. The lakes have grown more dilute and acidic with time, accumulated dissolved organic carbon and undergone a transient rise in nitrogen concentration, all as a result of successional changes in surrounding vegetation and soils. Similar trends are evident from fossil diatom stratigraphy of lake sediment cores. These results demonstrate a tight hydrologic coupling between terrestrial and aquatic environments during the colonization of newly deglaciated landscapes, and provide a conceptual basis for mechanisms of primary succession in boreal lake ecosystems.

Infrared dielectric anisotropy and phonon modes of sapphire

Abstract: Spectroscopic ellipsometry in the infrared spectral range is used for comprehensive analysis of the anisotropic dielectric response of sapphire. We determine the ordinary and extraordinary infrared complex dielectric functions as well as all infrared-active phonon modes of single crystal $\ensuremath{\alpha}\ensuremath{-}{\mathrm{Al}}_{2}{\mathrm{O}}_{3}$ for wavelengths from 3 to 30 \ensuremath{\mu}m. Data were acquired from high-symmetry orientations of a-plane and c-plane surfaces cut from bulk crystals. A simple classification scheme is developed, which allows identification of the total reflection bands for p- and s-polarized light in anisotropic materials with multiple phonon branches. We employ a factorized form of the dielectric function for superior best-fit calculation of the infrared ellipsometry spectra adjusting frequencies and damping parameters of the transverse and longitudinal phonon modes with ${A}_{2u}$ and ${E}_{u}$ symmetry separately. A generalized Lowndes condition for the damping parameters is derived and found satisfied for the ${A}_{2u}$ and ${E}_{u}$ branches. Excellent agreement with phonon mode literature values is obtained, and improper use of selection rules reported previously for calculation of the sapphire dielectric functions is revised [Harman, Ninomiya, and Adachi, J. Appl. Phys. 76, 8032 (1994)]. The dielectric function model will become useful for infrared ellipsometry investigation of multiple-layer structures grown on $\ensuremath{\alpha}\ensuremath{-}{\mathrm{Al}}_{2}{\mathrm{O}}_{3}$ substrates such as group-III nitride heterostructures.

Intrinsic ferroelectric coercive field

Abstract: The Landau-Ginzburg theory of ferroelectricity predicts the intrinsic coercive field for polarization reversal, but the observed extrinsic coercive field is always much smaller as a result of nucleation, dynamic processes not covered by the static theory. We have realized the intrinsic coercive field for the first time, in two-dimensional Langmuir-Blodgett polymer films as thin as 1 nm. The measured coercive field is in good agreement with the theoretical intrinsic value, exhibits the expected dependence on temperature, and does not depend on thickness below 15 nm.

Transgene and transposon silencing in Chlamydomonas reinhardtii by a DEAH-box RNA helicase.

Abstract: The molecular mechanism(s) responsible for posttranscriptional gene silencing and RNA interference remain poorly understood. We have cloned a gene (Mut6) from the unicellular green alga Chlamydomonas reinhardtii that is required for the silencing of a transgene and two transposon families. Mut6 encodes a protein that is highly homologous to RNA helicases of the DEAH-box family. This protein is necessary for the degradation of certain aberrant RNAs, such as improperly processed transcripts, which are often produced by transposons and some transgenes.

First-order transition in confined water between high-density liquid and low-density amorphous phases.

Abstract: Supercooled water and amorphous ice have a rich metastable phase behaviour. In addition to transitions between high- and low-density amorphous solids1,2, and between high- and low-density liquids3,4,5,6,7,8, a fragile-to-strong liquid transition has recently been proposed9,10, and supported by evidence from the behaviour of deeply supercooled bilayer water confined in hydrophilic slit pores11. Here we report evidence from molecular dynamics simulations for another type of first-order phase transition—a liquid-to-bilayer amorphous transition—above the freezing temperature of bulk water at atmospheric pressure. This transition occurs only when water is confined in a hydrophobic slit pore12,13,14 with a width of less than one nanometre. On cooling, the confined water, which has an imperfect random hydrogen-bonded network, transforms into a bilayer amorphous phase with a perfect network (owing to the formation of various hydrogen-bonded polygons) but no long-range order. The transition shares some characteristics with those observed in tetrahedrally coordinated substances such as liquid silicon15,16, liquid carbon17 and liquid phosphorus18.