bluuebunny/crossref_metadata_2025 huggingface dataset:
MÁQUINA CLASIFICADORA DE FLORES: DISEÑO Y CONSTRUCCIÓN
Authors: Martínez Freddy , Hernandez David , Cárdenas Herrera Pedro F.
Published: September 2017

Las máquinas clasificadoras tienen como objetivo principal optimizar el proceso de clasificación de cualquiera que sea el producto con el que trabajan, es decir, mejorar los resultados, disminuir los gastos y aumentar la velocidad del proceso. Este documento presenta el proceso de diseño y construcción de una máquina de clasificación de flores, la cual hace uso de técnicas de visión de máquina e inteligencia artificial. Esta máquina fue proyectada para desempeñarse bajo las condiciones ambientales de las salas de pos-cosecha en los invernaderos de la sabana de Bogotá.Palabras clave: Automatización de procesos agro-industriales, clasificación de flores, máquina clasificadora, visión artificial.
ANÁLISIS BIOMECÁNICO DE EL GESTO TÉCNICO EN BARRAS PARALEAS EN LA GIMNASIA OLÍMPICA
Authors: Santafé Ramón Yesid , Muñoz Luis Alberto , Mendoza Luis Enrique
Published: September 2017

El presente artículo muestra los resultados iniciales del análisis biomecánico para estudio del gesto técnico en barras paralelas en deportistas de alto rendimiento en gimnasia olímpica. Se presentan medidas tales como: distancia, trayectoria y velocidad del movimiento. Además se muestra el seguimiento del movimiento y los análisis estáticos del movimiento usando el software Kinovea. Se demuestra que el software permite realizar análisis biomecánico en movimiento de barras paralelas en gimnasia olímpica.Palabras clave: Biomecánica, Gesto Técnico, Cinemática.
ANÁLISIS DE CRITICIDAD Y ÁRBOLES DE DIAGNÓSTICO DE FALLAS PARA TRANSFORMADORES DE POTENCIA
Authors: Salamanca Jaimes Jesus Enrique , Velazco Ochoa Jesus Abelardo , Acevedo Camacho Eduar Alberto
Published: September 2017

El desarrollo de este artículo está dirigido a plantear el análisis de criticidad como modelo de jerarquización en subsistemas donde intervienen equipos de patio de subestaciones eléctricas propiedad de Centrales Eléctricas del Norte de Santander SA ESP. Este análisis es replicable a otros subsistemas y está basado en la recopilación de información de un grupo de trabajo específico con amplia experiencia en el mantenimiento de los activos objeto de estudio. Además de este análisis, se propone la implementación de árboles de diagnóstico de fallas para transformadores de potencia como herramienta fundamental en el análisis predictivo de fallas en este tipo de activo, cuya operación es fundamental para ofrecer un servicio continuo y de calidad.Palabras clave: Activos, análisis de criticidad, diagnóstico de fallas, mantenimiento.
COMPARATIVE STUDY ON READING COMPREHENSION BETWEEN STUDENTS OF JUNIOR HIGH SCHOOLS IN CITY AND RURAL AREA
Authors: Sholihah Lilis -
Published: September 2017

This study is aimed to: (1) find out the differences on reading comprehension between students of junior high school in city and rural area, (2) to find out factors that causes differences on reading comprehension between students in city and rural area. This resarch was carried out in SMPN 1 Serang, SMPN 1 Cilegon, SMPN 1 Picung and SMPN 1 Banjarsari. The method used was quantitative method in the form of comparative study. The writer used Ex Post Facto Design in this research. The population of the research was all the third year students of those four schools. The sampling technique was purposive sampling. The writer took 80 students for the sample. The instruments for collecting data were questionnaire, interview, test and also unstructured observation. The technique used to analyze data was T-Test separated variance and polled variance. The result of the study showed that there was a significant difference of students reading comprehension between students in city and rural area. It can be seen from the result of the test. Based on questionnaire which were given to the students and interview for the teacher, the researcher could find out the factors that cause differences on reading comprehension between students in city and rural area, such as the students’ interest, motivation of students, teaching methodology, reading material, vocabulary mastery, and culture.
THE INFLUENCE OF USING SKIMMING TECHNIQUE TOWARD THE STUDENTS’ READING COMPREHENSION AMONG THE ELEVENTH GRADERS OF SMK N 3 METRO
Authors: - Eka Yuniasih
Published: September 2017

The purpose of this research was to implement the skimming technique and analyze its influence in the student comprehending reading texts at the eleventh grade (XI TKJ) of SMK N 3 Metro. In this research the researcher gave pretest to know the students’ ability in understanding reading texts and posttest to know the result of the students’s ability in reading text after giving the skimming technique.This research was quantitative research which had been conducted in SMK N 3 Metro at the class XI TKJ and followed by 70 students as the sample. The tehnique sampling was cluster random sampling. In collectting the data the researcher used test. The researcher used the test to get the data of student’s reading comprehension through the questions which consisted of 30 multiple choices  about the reading text. This test was used to figure out whether the skimming technique was suitable and could be used by the students in comprehending the reading texts. The analysis which was used by the researcher was t-test. Finally, the data indicates that t observed  = 23.945 is higher than t table = 2.99. Therefore, it can be concluded that Ha is accepted and Ho is rejected. It means that the skimming technique influences the students’ reading comprehension at the eleventh graders of SMK N 3 Metro in the academic year of 2010/2011.
DEVELOPING ENGLISH LEARNING MATERIAL FOR SPEAKING SKILL BASED ON PROBLEM -BASED LEARNING (PBL) AT FIRST SEMESTER OF THE EIGHTH GRADE OF JUNIOR HIGH SCHOOL
Authors: - Hidha Fajarwati , - Amirudin Latif
Published: September 2017

The objective of the study is to develop practical English speaking materials by using Problem Based Learning (PBL). The design of the study is research and development which attempts to develop descriptive and recount text for speaking materials. The steps of the research and development for the materials include self evaluation, expert review, one-to-one try out, small group try out, field test, and final product. The subjects of this research are the eighth grade students of State Junior High School 6 Metro. The result of the study is English learning material for speaking skill based on problem based learning.
DEVELOPING EVALUATION INSTRUMENT OF READING FOUR TEST FOR UNIVERSITY STUDENT
Authors: - Refai -
Published: September 2017

Abstract: The objective of the study was to develop the evaluation Instrument of reading four test . The development of such instrument is a valuable effort to measure the students’ mastery of the reading skill and to improve the quality of the evaluation instrument which is produced by the teacher. Before the teacher develop the reading evaluation instrument, he had cultivated the previous test instrument to analyze the weakness and the strength of the implemented test instrument. After that, the teacher started to develop a prototype which has been modified by the teacher himself. Then, he administered the first try out to the English students of semester VII and collecting some inputs and critics of the modified reading test instrument after the students finished doing the test. The result of the test together with the students’ critics and inputs were used to rebuild the reading test intrument better. At last, the teacher has developed the evaluation instrument of reading test for students of semester VII in Muhammadiyah University of Metro.
Promoting Picture Word Inductive Model (PWIM) to Develop Students’ Writing Skill
Authors: Novia Fitri
Published: September 2017

Abstract: The objective of this study was to find out whether or not there was significant difference between students who were taught using picture word inductive model (PWIM) and that of those who were not. The experimental method was used to conduct the study. The population of this study was the eighth grade students in SMP N 1 Sirah Pulau Padang.  Out of this pouplation, 68 students were taken as a sample and were divided  equally into two groups by using purposive sampling method. Therefore, class VIII 1 was the experimental group whereas VIII 3 as the control group, each of them consists of 34 students. The data were collected by asking students to write descriptive paragraph. To find out the validity, content validity was used. Inter-rater reliability was used to find out the reliability. T-test was used to analyze the data. Based on the result, the value of t-obtained was 3.155, at the significant level p<0.05 in two tailed testing with do = 66, the critical value of t-table = 1.9966. Since the value of t-obtained was higher than t-table, the Null Hypotheses (Ho) was rejected and Alternative Analysis (Ha) was accepted. It meant that there was significant difference between students who were taught using picture word inductive model (PWIM) and that of those who were not. In conclusion, PWIM could help students to develop writing skill. Key Word: Writing skill, Picture Word Inductive Model (PWIM).
THE EFFECT OF USING FLASH CARD AND PICTURE STORY IN VOCABULARY MASTERY TO THE SEVENTH GRADER OF SMP PGRI 1 MARGATIGA
Authors: - Khoirul Hidayat
Published: September 2017

Based on the content standard, junior high school students are hoped to master vocabulary about 1000 words, so they can understand the conversation. But it fact, most of the students in junior high school do not master vocabulary well. So, the teacher should be able to choose a good media to help students to increase their vocabulary. In this case, flash card with picture story is two of media that can be used to transfer vocabulary material for the students. The objective of this research is to find the significant differences of using flash card with picture story in vocabulary, and to find which medium is more effective to use as media in vocabulary. This research was true experiment design. Pre test and post test were use to collect the data. There are two problems of the study, (1) are there any significant differences between flash card with picture story in vocabulary mastery for the seventh grade students in SMP PGRI 2 Margatiga academic years 2013/2014?, (2) which one is more effective media in vocabulary learning process, is it flash card or picture story at seventh grade of SMP PGRI 2 Margatiga, academic years 2013/2014?. As a source of data, the researcher utilized flash card with picture story to teach vocabulary for the students. The media help students to learn vocabulary easier and more interesting to understand the subject, so their vocabulary would increase. The result of the research, it was found that the mean score of picture story in pre test is 53,86, in treatment is 81, and in post test 85,33. Meanwhile the mean score of the flash card media in pre test 59,33, in treatment is 73,5, and in post test is 80,66. It means that the student’s vocabulary has increased, and there is significant difference of using picture story and flash card in vocabulary instruction, and picture story was more effective to use in vocabulary instruction.
Visibilización y valorización de la agricultura familiar periurbana. Intervenciones de políticas públicas en el partido de La Matanza
Authors: Feito Carolina
Published: September 2017

Analizamos intervenciones sociales para agricultores familiares periurbanos de La Matanza y articulaciones entre instituciones que implementan políticas públicas para visibilizar estas producciones. Se utilizó metodología cualitativa realizando trabajo de campo etnográfico y relevamiento de información secundaria. Intentamos demostrar que las articulaciones entre distintas instituciones y actores en la implementación de políticas para el sector son aún incipientes y no visibilizan ni valorizan sus potencialidades reales existentes. Descubrimos interfaces1 entre distintos actores: productores, extensionistas e implementadores, así como intervenciones para incorporación de tecnologías apropiadas. Concluimos que las intervenciones operan en una arena de conflicto y disputa en la implementación de políticas y programas de desarrollo.
Procesos organizativos y políticas públicas destinadas a productores familiares del sur del Área Metropolitana (provincia de Buenos Aires, Argentina), 2002-2015
Authors: Seibane Cecilia , Ferraris Guillermina
Published: September 2017

El objetivo del trabajo es caracterizar a las organizaciones de pequeños productores familiares en el sur del Área Metropolitana de Buenos Aires (AMBA Sur), en los partidos de La Plata, Berazategui y Florencio Varela. La metodología utilizada es de tipo cualitativo. Los resultados muestran que las políticas públicas implementadas hacia el sector hasta el año 2015 promovieron instancias que facilitaron la organización y el fortalecimiento de estos productores, dando lugar a distintas formas asociativas. La tierra y la comercialización son problemáticas muy sentidas. En la actualidad, estas organizaciones participan en mesas regionales, generando y fortaleciendo instancias organizativas territoriales cada vez más articuladas.
Interview with Nancy Down Head Librarian at Bowling Green State University Popular Culture Library, Ohio;
Authors: Werts Cybèle Elaine
Published: September 2017

This interview with Nancy Green, Head Librarian of the Popular Culture Library, Bowling Green University, describes one of the largest and most comprehensive special collection of popular culture which has been digitized and put into a searchable database system.
Resources on the Net: Past, Present, and Future of Academic Libraries
Authors: Bober Chris
Published: September 2017

The following is a continuation of Resources on the Net: Past, Present, and Future of Academic Libraries, published in the Summer 2009 issue of Education Libraries.
Book Reviews
Authors: Keiser Barbie E. , Moore Celeste , Niedbala Anne , Shen Julie , Bollinger Elizabeth J.
Published: September 2017

[...]
Remembering Cybèle Werts
Authors: Snider Jacqueline
Published: September 2017

Cybèle Werts passed away on October 2, 2010 at the age of 47. Cybèle was a dynamic, energetic, and vivacious person. When I met her several years ago at an SLA conference, she was talking a mile a minute; ready for any challenge. [...]
Activities and Strategies for the Inclusion of a K-12 Educational Component in Digitization Grant Projects of Academic Libraries
Authors: Teel Linda
Published: September 2017

This article seeks to explore and discuss activities and strategies for including a K-12 educational component in digitization grant projects in academic libraries. The article is based on cases studying the K-12 educational component of the three following grants awarded to East Carolina University Joyner Library by North Carolina Exploring Cultural Heritage Online (NC ECHO) grant program: Digitizing Eastern North Carolina History, Fiction and Artifacts: The Eastern North Carolina Digital Library (http://digital.lib.ecu.edu/historyfiction/), Seeds of Change: The Daily Reflector Image Collection (http://digital.lib.ecu.edu/reflector/), and Ensuring Democracy Through Digital Access: North Carolina Government Publications Collection (beta testing). Planning, budgeting, implementation, promotion and lessons learned are discussed offering first-hand experiences in effective methods to integrate activities and strategies into digitization projects providing access to useful resources for all users with a focus on K-12 educators and students. The author‘s interest in this topic is based on cumulative experiences of involvement in the listed digitization grant projects as a private investigator and as an educational consultant of the above grants. Lessons learned are highlighted providing readers with specific, valuable details for consideration to improve future digitization projects.
Software Review: A Review of the Plone Content Management System
Authors: Bollinger Stephen P.
Published: September 2017

Web content management systems (CMSs) are tools to help efficiently manage modern websites. Broadly defined, CMSs are database-driven software packages that allow people who are not HTML experts to create and edit website content, manage revisions and approvals for content, and help reduce the workload of maintaining a website. Within the past five years open source content management systems, created and maintained by a community of software developers and available without charge, have matured to become viable options for libraries that are not information technology juggernauts. Plone1, now in its fourth major release, is one such content management system that is now in wide use by libraries. [...]
Book Reviews
Authors: Keiser Barbie , Lestini Paula
Published: September 2017

[...]
Information Anxiety and African-American Students in a Graduate Education Program
Authors: Fields Katopol Patricia
Published: September 2017

Library anxiety has been cited as one factor affecting academic performance, but library use is only part of obtaining information for academic needs. This paper expands the concept of library anxiety to information anxiety by an examination of the information behavior of black graduate students when using a variety of information resources, including electronic and human. Findings indicate that information anxiety is a continuous element of minority students’ information behavior and creates a barrier to obtaining and using information for academic work.
Information Literacy Outreach: Building a High School Program at California State University Northridge
Authors: Meyers Martin Coleen , Garcia Eric P. , McPhee Marc
Published: September 2017

University and secondary school educators recognize many high school students will undertake a post-secondary education but find themselves unprepared for the academic demands once they arrive on campus. Although many high school students appear to possess basic abilities in retrieving information, particularly when searching the Internet, they often lack the critical evaluation skills needed to succeed at the college level (Jackson & Hansen, 2006). Developing the necessary information literacy skills among high school students to support a successful transition to college is a unique undertaking for any institution. The authors provide a case study of an outreach effort between an academic library and an urban high school during challenging budgetary times. Lessons learned from the development of their information literacy instructional program and the instructional tools created will be discussed. Student outcomes within the collaboration which include the development of research and critical thinking skills necessary to succeed after high school will be addressed as well. This collaboration may serve as a model for other institutions developing similar programming.
From Pedagogical Museum to Instructional Material Center: Education Libraries at Teacher Training Institutions, 1890s to 1970s
Authors: Attebury Ramirose , Kroth Michael
Published: September 2017

The development of education libraries cannot be understood outside the context of education history. Changes in educational practices and technology spurred three phases of development in the history of education libraries. Early examples, often called curriculum laboratories, developed as spaces to create educational materials where limited numbers existed. As standardized curriculum grew, common laboratories gave way to curriculum materials centers, which housed materials so that future teachers could preview them. The rise of audio-visual equipment transformed education libraries once again into centers housing a variety of instructional materials. This paper traces the development of education libraries through these three phases.
Education Division Guest Editorial: 40th Anniversary of the Special Libraries Association Education Division
Authors: Dratch Gladys I. , Garson Deborah S.
Published: September 2017

This year, 2014, celebrates the 40th anniversary of the SLA Education Division. As the Division was founded in June 1974 at the Annual Conference of the Association in Toronto, Canada, it was appropriate that we celebrated the 40th Anniversary at the June 2014 conference in Vancouver, Canada. [...]
Worldwide Diffusion of Corporate Governance (CG) Regulations and Practices: A Literature Review
Authors: Ahmad Zubair , Mahmood Zeeshan
Published: September 2017

Research objectives: The main objective of this paper was to understand the diffusion of CG codes around the world. More specifically this paper examined what types of CG codes have emerged around the world? What causes the diffusion of shareholder centric model of CG around the world? What areas are still unexplained to better understand the diffusion of CG?

Findings: This paper presented that pure economics and legitimacy reasons alone or together are not sufficient to explain the dynamics of how corporate governance reforms emerged and developed in different contexts. This study assumes that it is important to move the debate beyond the efficiency/legitimacy and convergence/divergence dichotomy and pay more attention to the process of emergence and development of corporate governance reforms.

Implications: Prior institutional research ignores countries' internal dynamics that can play an important role in shaping corporate governance reforms. The corporate governance model cannot exist in isolation; each country has its own unique institutional arrangements and can influence the process of diffusion. There is some consensus amidst corporate governance scholars that "the-one-size-fits-all" rule is flawed, and thus a wide diversity of approaches of corporate governance should be expected due to vast differences in national contexts where firms are embedded (Cuervo, 2002, Reaz and Hossain, 2007). Policy makers and researchers should consider broader institutional dynamics related to macro and micro institutional processes while developing and understanding CG diffusion around the world.
Financial Analysts' Processing of Financial Reporting Information in Emerging and Frontier Markets
Authors: Jehu Philip , Ibrahim Mohammad Azhar
Published: September 2017

Objective: The purpose is to establish the relationship between the analysts' stock valuation, the reporting environment and the stock recommendations. And to investigate the process of incorporating both quantitative and qualitative information into their forecasts.

Methodology: The research will be archival, obtaining historical information from DataStream, Stock Exchanges and MSCI. A survey will also be carried out to corroborate findings, as the analysts' valuation process may not be obtained through desk research.

Results: The results are expected to show evidence for the incentive conflicts of the analysts' decisions with regards to the peculiarities of the macroeconomic environments under consideration.

Implication: The write up has implications for sell-side analysts where they have perceived incentive conflicts when they make recommendations. The research contributes to the argument on the conflicts of interest analysts face in forecasting earnings and making recommendations within the markets peculiar environment.
Financial Sharing in Infrastructure Joint Venture Projects
Authors: Romeli Norsyakilah , Muhamad Halil Faridah , Ismail Faridah , Wena Dhelbi Jacqueline
Published: September 2017

Objective: The purpose of this paper is to identify the financial sharing limitation in contractor’s infrastructure project in joint venture implementation. 

Methodology: Using the quantitative method, the questionnaires, constructed based on external and internal variables were distributed to the selected respondents. The analysis of the data is conducted with simple SPSS analysis to identify the mean, median and standard deviation. The ranking of the variables is drawn from the results.

Results: The outcome of this research has found that the crucial external limitations are penalty to the foreigners and that market legislation requires limitation in the sharing proportion. Meanwhile, for the internal limitation the ownership control and rate fluctuation should be followed with certain marking lines.  

Implication: Thus, this paper stimulates the joint venture contractor to set up the post financial remedial plan once one of the collaborative partners breaches the agreement on the joint venture due financial limitation.
Determinants of Efficiency in Health Sector: DEA Approach and Second Stage Analysis
Authors: Adil Rabia , Abbas Muhammad , Yaseen Asif
Published: September 2017

There are several factors that influence the performance of health structure. Achieving efficiency in healthcare sector is the goal of every economy in the world. To accomplish this end, it is dominant to find out the efficiency. The present study is designed to measure the efficiency of selected Asian countries. A Non-parametric data envelopment analysis input-oriented approach under constant returns to scale is applied to measure the technical efficiency for the time span of 2012. By applying CRS model of DEA, 11 countries out of 26 are found to be efficient. The study provides suggestions to enhance the efficiency as well productivity of these Asian countries.
Stress and velocity fields in glaciers: Part I. Finite-difference schemes for higher-order glacier models
Authors: Colinge Jacques , Blatter Heinz
Published: September 2017

The set of force equations and stress strain-rate relations for ice masses can be solved with the method of lines and shooting the stress-free conditions at the free surface. Single- and multiple-shooting schemes with fixed point or Newton iterations for solving the stress equations including the deviatoric stress gradients are described and their performances arc discussed. The single-shooting Newton iteration proved to be the fastest seheme for typical valley glaciers, although its horizontal grid limitation is restrictive. Grid resolution can be improved substantially with a multiple-shooting scheme but computation time and storage requirements increase substantially. The Newton iteration allows the handling of mixed basal boundary conditions, partly basal velocity and partly basal shear traction being prescribed. A stick slip free gravity flow illustrates the performance of the scheme.
Diffusion of isotopes in the annual layers of ice sheets
Authors: Nye J. F.
Published: September 2017

The annual layering in the Greenland and Antarctic ice sheets revealed by the b 0 record becomes less distinct with depth because of self-diffusion. However, the calculated diffusion rates are loo slow to explain die observations. It is suggested that the presence of veins of liquid water increases the effective diffusion constant by a factor of about 20.
Depth-hoar growth rates near a rocky outcrop
Authors: Arons E. M. , Colbeck S. C. , Gray J. M. N.T.
Published: September 2017

Observations of slab-avalanche releases in alpine terrain have led to the hypothesis that rocky outcrops can influence the spatial distributions of temperature and heal flow in dry alpine snow covers and Unis control the local distribution of depth hoar. We investigate the effects of terrain on crystal growth by using a two-dimensional finite-clemcnl model of heal How coupled with a model of crystal growth from vapor. We used the model to examine the influence of snow properties, terrain geometry and snow depth on this phenomenon. The efleel is stronger in the early winter than in the late winter, because the rock has then had time to cool. In all cases, we found that depth-hoar growth occurs preferentially over the rock. This suggests that snow-pit investigations made over soil can he misleading if rocky outcrops are present.
A snow-transport model for complex terrain
Authors: Liston Glen E. , Sturm Matthew
Published: September 2017

As part of the winter environment in middle- and high-latitude regions, the interactions between wind, vegetation, topography and snowfall produce snow covers of non-uniform depth and snow water-equivalent distribution. A physically based numerical snow-transport model (SnowTran-3D) is developed and used to simulate this three-dimensional snow-depth evolution over topographically variable terrain. The mass-transport model includes processes related to vegetation snow-holding capacity, topographic modification of wind speeds, snow-cover shear strength, wind-induced surface-shear stress, snow transport resulting from saltation and suspension, snow accumulation and erosion, and sublimation of the blowing and drifting snow. The model simulates the cold-season evolution of snow-depth distribution when forced with inputs of vegetation type and topography, and atmospheric foreings of air temperature, humidity, wind speed and direction, and precipitation. Model outputs include the spatial and temporal evolution of snow depth resulting from variations in precipitation, saltation and suspension transport, and sublimation. Using 4 years of snow-depth distribution observations from the foothills north of the Brooks Range in Arctic Alaska, the model is found to simulate closely the observed snow-depth distribution patterns and the interannual variability.
Estimation of hydraulic properties of subglacial till from ploughmeter measurements
Authors: Fischer Urs H. , Iverson Neal R. , Hanson Brian , LeB. Hooke Roger , Jansson Peter
Published: September 2017

Force variations on a "ploughmeter" and fluctuations in subglacial water pressure have been measured in the same borehole at Storglaciaren, Sweden, to investigate hydraulic properties of the basal till layer. A strong inverse correlation of the pressure and force records, in conjunction with a significant lime lag between the two signals, suggests that pore-water pressures directly affect the strength of the till. Variations in sub-glacial water pressure result in potential gradients across the water till interlace at the bottom of the borehole that drive pressure waves downwards through the till layer when the borehole water level is high and back upwards when the water level is low. Analysis of the propagation velocity of this pressure wave indicates that the hydraulic diffusivity of Storglaciaren till is in the range 1.9−3.6 x 10−6m2s−1,in good agreement with estimates obtained in the laboratory. Hydraulic conductivity values associated with these difrusivities are between 10−9 and 10−8ms−1 and thus are well within the range of values for other glacial tills.
Elevation and volume changes on the Harding Icefield, Alaska
Authors: Adalgeirsdóttir G. , Echelmeyer K. A. , Harrison W. D.
Published: September 2017

Airborne surface elevation profiles of the Harding Ice field, south-central Alaska, were made in 1991 and 1996. Thirteen glaciers were profiled, along with the tipper region of the icefield. The profiles were compared to U.S. Geological Survey topographie maps made in the 1950s, to obtain elevation and volume changes. Comparison of the changes for the different glaciers shows no significant correlation between volume change and the type of glacier or characteristics such as location, aspect, size, slope or terminus changes. Estimated total volume change tor this ~43 year period is about -34 km3, which corresponds to an area-average elevation change of-21 m. The estimated error in this elevation change of 5 m is mainly due to errors in the maps at higher elevations. Our measurements provide an accurate baseline against which future determinations of volume change can be made.
Ice-stream surface texture, sticky spots, waves and breathers: the coupled flow of ice, till and water
Authors: Hindmarsh Richard C. A.
Published: September 2017

This paper addresses the coupling of flows of ice, till and water, and the issue of whether such coupling provides mechanisms for meso-scale (kilometres to tens of kilometres) variability in ice-sheet flow and texture. The question of whether effective pressures at the ice-bed interface are statically or hydraulically controlled is examined in this paper. The answer is scale dependent, and has a significant effect on the relationship between ice surface and basal topography.

The consequences of these considerations on till flow, coupled ice–till flow and coupled ice, till and water flow are examined. An analysis of till-flow kinematics and shock formation is carried out. The linear stability of coupled long-wavelength ice-till flow is analysed, and regions in parameter space where this flow is unstable, with rather small rate constants are found. Upstream-moving ice surface waves are predicted. The linear stablity of coupled ice–till–water flow is examined, where water flow is modelled using a basal flow system with effective-pressure-dependent properties. Again, regions in parameter space where the system is linearly unstable are found, this time with relatively rapid rate constants. The water pressure exhibits “breather” modes.

These analyses assume that there is a substantial basal traction. A problem with models of ice streams wholly restrained at the side is identified: they seem to predict erosion rates which are unfeasibly large.

There appears to be sufficient variability in the ice–till– water system to potentially explain texture in ice-stream surfaces, variations in ice-stream thickness of tens of metres not directly relatable to topography, and waves moving upstream or downstream. Most importantly, the ice-stream–bed system is shown to exhibit meso-scale variability simply by coupling ice flow according to the shallow-ice approximation, till flow according to the hydrostatic thin-till approximation and water flow according to an effective-pressure-dependent hydraulics.
Ring-shear studies of till deformation: Coulomb-plastic behavior and distributed strain in glacier beds
Authors: Iverson Neal R. , Hooyer Thomas S. , Baker Robert W.
Published: September 2017

A ring-shear device was used to study the factors that control the ultimate(steady) strength of till at high shear strains.Tests at a steady strain rate and at different stresses normal to the shearing direction yielded ultimate friction angles of 26.3° and 18.6° for tills containing 4% and 30% clay-sized particles, respectively Other tests at steady normal stresses and variable shear-strain rates indicated a tendency for both tills to weaken slightly with increasing strain rate. This weakening may be due to small increases in till porosity.

These results provide no evidence of viscous behavior and suggest that a Coulomb-plastic idealization is reasonable for till deformation. However, viscous behavior has often been suggested on the basis of distributed shear strain observed in subglacial till. We hypothesize that deformation may become distributed in till that is deformed cyclically in response to fluctuations in basal water pressure. During a deformation event, transient dilation of discrete shear zones should cause a reduction in internal pore-water pressure that should strengthen these zones relative to the surrounding till, a process called dilatant hardening. Consequent changes in shear-zone position, when integrated over time, may yield the observed distributed strain.
Determining basal ice-sheet conditions in the Dome C region of East Antarctica using satellite radar altimetry and airborne radio-echo sounding
Authors: Siegert Martin J. , Ridley Jeffrey K.
Published: September 2017

Large subglacial lakes manifest themselves as flat regions on the ice surface. ERS-1 satellite radar altimetry of the Dome C region of East Antarctica was analyzed to correlate unusually flat areas on the ice surface with known locations of subglacial lakes identified from airborne radio-echo sounding (RES) data. The mean length of subglacial lakes which have an expression in the ice-sheet surface was ~8.3 km, whilst those that did not exhibit a surface morphological manifestation had a mean length of ~3.3 km. Thus, lakes up to about 4 km in length arc unlikely to be detected from satellite radar altimetry of the ice surface. Given that the spacing of radio-echo flight tracks within the SPRI-NSF-TUD Antarctic database is 50-100 km in many areas, a number of subglacial lakes probably lie undetected beneath the ice sheet. RES information from two large, flat surface regions within Dome C, and a further flat area located at 80° S, 127° E, indicates the absence of subglacial lakes beneath the ice-surface features. However, these areas are characterised by relatively strong radio-echo returns which may indicate the presence of water-saturated basal sediments. We suggest that (1) blankets of water-saturated basal sediments may cause similar surface morphological features to those produced by subglacial lakes; and (2) misidentification of subglacial lakes from satellite altimeter observations of the ice-sheet surface is possible without the support of RES information relating to the ice-sheet base. Furthermore, our study indicates a lack of subglacial lake signals from RES data over relatively thick regions of East Antarctica such as the Adventure Subglacial Trough. We conclude that subglacial water produced in such regions may be transported by a basal hydrological system, driven by overburden pressure, to less thick regions of the ice sheet where subglacial lakes have been identified.
2 m temperatures along melting mid-latitude glaciers, and implications for the sensitivity of the mass balance to variations in temperature
Authors: Greuell Wouter , Böhm Reinhard
Published: September 2017

In calculations of the variation in the 2 m temperature along glaciers, the lapse rate is generally assumed to be constant. This implies that the ratio of changes in the 2 m temperature above a glacier to changes in the temperature outside the thermal regime of that glacier (“climate sensitivity”) is equal to 1. However, data collected during the ablation season on several mid-latitude glaciers show that this sensitivity is smaller than 1. The lowest measured value (0.3) was obtained on the tongue of the Pasterze, a glacier in Austria. The measured temperature distribution along the Pasterze cannot be described by a constant lapse rate either. However, there is almost a linear relationship between potential temperature and the distance along die glacier. This paper introduces a simple, analytical, thermodynamic glacier-wind model which can be applied to melting glaciers and which explains the observed “climate sensitivities” and temperature distributions much better than calculations based on a constant lapse rate.

This way of modelling the 2 m temperatures has implications for the sensitivity of the surface mass balance to atmospheric warming outside the thermal regime of the glacier. The magnitude of this sensitivity is computed with a surface energy-balance model applied to the Pasterze. When a constant lapse rate is used instead of the proposed glacier-wind model to compute changes in the 2 m temperature along the glacier, the negative change in mass balance due to 1°C warming is overestimated by 22%.
A simple model for the influence of push-morainal banks on the calving and stability of glacial tidewater termini
Authors: Fischer Mark P. , Powell Ross D.
Published: September 2017

Push-morainal banks at the grounding lines of tidewater termini of temperate glaciers are the source of two types of restraining forces operating at the glacier terminus. Horizontal normal forces derive from the lateral support and transport of the bank of sediment at the terminus, whereas a horizontal shear force operates along the base of a bank pushed in front of an advancing glacier. The simple model we present suggests that bank-related restraining forces are significantly larger than the restraining force derived from the hydrostatic pressure of water adjacent to the submerged terminus of a glacier. During glacier advance, restraining forces continually increase, resulting in decreasing flow rates, glacier thickening and the eventual cessation of advance. During retreat, restraining forces continually decrease, resulting in increasing flow rates, glacier thinning and the potential for unstable, rapid, sustained retreat. The normal, seasonal, oscillatory advance retreat cycle of a glacier is moderated by restraining forces associated with push moraines. Unstable retreat is likely initiated when bank-related restraining forces fall below some threshold value during the seasonal retreat cycle. Calving is not a primary cause of glacier retreat, but is more likely a short-term response to increased flow rates. Increased flow rates result in glacier thinning and an approach toward buoyancy, both of which fluctuate seasonally in accordance with bank-related restraining forces.
Thin-sectioning of wet snow after flash-freezing
Authors: Brzoska Jean-Bruno , Coléou Cécile , Lesaffre Bernard
Published: September 2017

A new method for preparing thin sections of wet snow is described. Samples are flash-frozen to immobilise the liquid water content (LWC). Next, the pore space is filled with ester, and the entire sample is frozen to a solid, sliceable block, Micrographs of slices are obtained using transmitted and specular illumination. The proportion of LWC is measured on the micrographs and compared with LWC measured independently using calorimetry. Section analysis is both facilitated and complicated by small bubbles which form during sample preparation. Flash-freezing and bubble formation are discussed theoretically.
Synthetic aperture radar interferometry over Rutford Ice Stream and Carlson Inlet, Antarctica
Authors: Frolich R. M. , Doake C. S. M.
Published: September 2017

We describe the calibration and interpretation of interferograms generated from ERS-1 synthetic aperture radar Single Look Complex (SAR.SLC) images of the Rutford Ice Stream area. Ground surveys provide over 100 tie-points with which to optimise the interferometric baselines that separate nominally repeated satellite orbits. Covariant tie-point errors are dealt with by constructing an error covariance matrix for the expected values of the unwrapped interferometric phases at the tie-points. With baseline parameters that minimise the weighted residual variance, rms tie-point residuals of less than 1 cm in slant range are obtained. These are attributed to a combination of interferometric phase noise, movement survey errors and inadequate slope information. The image set used is inadequate for isolating the influences of topography and movement, so the glaciological conclusions to be drawn are limited. Nevertheless, the interferograms confirm that the whole of the upper 50 km of Carlson Inlet flows at a speed less than a tenth of that of the neighbouring Rutford Ice Stream. Also confirmed are the entry of faster-moving ice into the lower reaches of Carlson Inlet and the position of part of the Carlson Inlet grounding line. In general, the distribution of the residuals suggests no significant differences in ice movement between 1978 and 1992. An exception is the neighbourhood of the shear margin between Rutford Ice Stream and Carlson Inlet, where inconsistencies between ground surveys over the periods 1984-86 and 1994-96 and interferograms from 1994 and 1996 suggest fluctuations in velocity of up to 10 m year−1.
Rapid sea-level rise from a West Antarctic ice-sheet collapse: a short-term perspective
Authors: Bentley Charles R.
Published: September 2017

Will worldwide sea level soon rise rapidly because of a shrinkage of the West Antarctic ice sheet (WAIS)? Here I give a personal perspective of that probability. The crucial question is not whether large changes in ice mass can occur, but how likely it is that a large, rapid change, say a several-fold increase in the 20th-century rate of about 2 mm a-1, will occur in the next century or two from a West Antarctic cause.

Twenty years ago Weertman proposed that a marine ice sheet is inherently unstable. But Weertman’s analysis was based on a simple model of a marine ice sheet that did not include fast-flowing, wet-based ice streams, which are now known to dominate the grounded ice sheet. Modern analyses do not definitively determine just how ice streams affect the stability of the WAIS, but it can at least be said that there is no compelling theoretical reason to expect a rapid rise in sea level from the WAIS triggered by ice-shelf thinning.

Of the three main ice-drainage systems in the WAIS, the one that flows into Pine Island Bay might be a particularly likely site for accelerated flow since there is no ice shelf to restrain the inflowing ice streams, yet measurements show that this system is not significantly out of mass balance. If the “Ross Embayment” system, which has undergone several sudden glacial reorganizations in the last thousand years, were unstable one might expect a history of large changes in the total outflow of ice into the Ross Ice Shelf, yet the total outflow in the “Ross Embayment” has remained relatively unchanged despite the large internal perturbations, a fact that, points to a stable, not an unstable, system. Study of the third major drainage from the WAIS, into the Ronne Ice Shelf, also suggests that there is no gross discordance between the present velocity vectors and flow tracers in the ice shelf, although the evidence is limited.

In the light of the evidence for recent stability, it is difficult to see how climate warming (whether anthropogenic or natural) could trigger a collapse of the WAIS in the next century or two. Thus, I believe that a rapid rise in sea level in the next century or two from a West Antarctic cause could only occur if a natural (not induced) collapse of the WAIS were imminent. Based on a concept of pseudo-random collapse once per major glacial cycle, I estimate the chances of that to be on the order of one in a thousand.
A new portable ice-core drilling machine: application to tephra studies
Authors: Casas J. M. , Sàbat F. , Vilaplana J. M. , Parés J. M. , Pomeroy D. M.
Published: September 2017

A new portable device for ice-core drilling, specially designed for thin tephra-layer sampling, was tested on the South Shetland glaciers during the 1994-95 Antarctic summer. The machine is based on a combination of the standard paleomagnetism drilling machine and a specially built drill-bit designed for ice-coring.
Reconnaissance Study of glacier energy balance in North Greenland, 1993–94
Authors: Braithwaite Roger J. , Konzelmann Thomas , Marty Christoph , Olesen Ole B.
Published: September 2017

Reconnaissance energy-balance studies were made for the first time at two sites in North Greenland to compare with conditions in West Greenland. The field experiments were planned to save weight because it is expensive to operate in North Greenland. The larger energy components (incoming radiation and ablation) were measured for 55 days altogether, and the smaller components were evaluated by indirect methods, e.g. turbulent fluxes are calculated from air temperature, humidity and wind speed, to save the weight of instruments. The energy-balance model is “tuned" by choosing surface roughness and albedo to reduce the mean error between measured ablation and modelled daily melting. The error standard deviation for ablation is only ± 5 kg m −2 d−1’, which is much lower than found in West Greenland, due to better instruments and modelling in the present study. Net radiation is the main energy source for melting in North Greenland but ablation is relatively low because sublimation and conductive-heat fluxes use energy that would otherwise be available for melting. There is a strong diurnal variation in ablation, mainly forced by variations in shortwave radiation and reinforced by nocturnal cooling of the ice surface by outgoing longwave radiation and sublimation. The model frequently predicts a frozen glacier surface at night even when air temperatures are positive.