215 research outputs found
Geochemical tools and paleoclimate clues : multi-molecular and isotopic investigations of tropical marine sediments and alpine ice
Submitted in partial fulfillment of the requirements for the degree of
Doctor of Philosophy at the Massachusetts Institute of Technology
and the Woods Hole Oceanographic Institution February 2006South American climate has undergone dramatic changes since the last glacial
period, as evidenced from Cariaco Basin (Venezuelan coast) and Peru Margin marine
sediment biomarker records. Compounds derived from vascular plant leaf waxes and
delivered to the marine sedimentary environment, including long-chain (C24-C32) nalkanoic
acids, were used as proxies for terrestrial vegetation type, aridity, and
atmospheric circulation. Marine biomarkers, such as sterols and phytol, were used to
reconstruct productivity in the Peru Margin upwelling zone, where sedimentary
conditions are not conducive to the preservation of foraminifera. Through the use of
organic molecular isotopic techniques and multi-molecular stratigraphy, a great deal can
be learned about communities of marine organisms and terrestrial plants that existed in
the past and the environments in which they lived.
Vascular plant leaf wax carbon and hydrogen isotopic records were generated
from n-alkanoic acids preserved in Cariaco Basin marine sediments. These records were
compared to previously established pollen and climate records and were found to parallel
local millennial-scale climate changes between the late Glacial and Preboreal periods,
which were characterized by migrations of the inter-tropical convergence zone.
Differences in δD between C16-C18 and C24-C30 n-alkanoic acids suggest a marine source
for the shorter chain lengths and a terrestrial source for the longer chains. Stacked δD
and δ13C records both exhibited isotopic enrichment during the late Glacial and Younger
Dryas periods and depletion during the Bølling-Allerød and Preboreal periods. If
interpreted as an aridity proxy, the δD record is in agreement with Cariaco Basin
sediment grey scale records, suggesting that the late Glacial and Younger Dryas were
more arid than the Bølling-Allerød and Preboreal periods. n-Alkanoic acid δ13C, which is
a proxy for C3 versus C4 plant type, indicates that C3 plants predominated in this area of
the tropics during warm and wet periods, such as the Bølling-Allerød and the Holocene,
and C4 plants proliferated during cooler and more arid periods, such as the Glacial and
Younger Dryas. The biomarker δ13C record agrees with pollen data previously developed
from Cariaco Basin sediments, confirming that leaf wax compounds preserved in marine
sediments can accurately record terrestrial vegetation changes.
Analytical methods utilizing stir bar sorptive extraction (SBSE) and thermal
desorption were developed and applied to investigate lipid organic matter in a suite of
alpine ice cores. These methods permit use of small volume (10-30 ml) samples, as
would be required for high-resolution down-core analyses. SBSE involves using a
polymer coated stir bar to extract organic matter from aqueous samples, after which it is
loaded directly into a thermal desorption unit and the organic matter transferred in its
entirety to a gas chromatograph inlet. To test these methods and the organic content of
tropical ice, post-industrial samples from two South American, two Asian, and one
African ice core were analyzed. Compounds identified in the modern ice core samples
included natural and anthropogenic biomarkers such as n-alkanes, n-alkanoic acids, nalkyl
amides and nitriles, polycyclic aromatic hydrocarbons (PAHs), and diterpenoids.
Variability in the distributions of these compounds between different cores demonstrated
that the lipid organic fraction in each core was representative of mostly local inputs. To
further investigate natural inputs, several pre-industrial samples were analyzed from the
Sajama ice core in the Andes and The Puruogangri core on the Tibetan Plateau. Inputs of
terrestrial vegetation combustion biomarkers such as PAHs, diterpenoids, and alkyl
amides were consistent with periods of enhanced aridity in each core. The results of this
investigation demonstrate the utility of the methodology, which could now be applied to
generate very high-resolution biomarker records from tropical ice cores.
Gas chromatography/time-of-flight mass spectrometry (GC/TOF-MS) was used to
generate a high-resolution, multi-molecular organic biomarker record from Peru Margin
sediments (~11oS, 252 m water depth) for the last 15 ka. Because of their position
beneath the oxygen minimum zone of a productive upwelling region, these sediments
contain a wealth of compounds that can be exploited as paleoclimate indicators. TOF-MS
and fast GC techniques allowed me to generate this record in a short amount of time and
without employing the traditional suite of purification techniques. Before about 9 ka,
organic carbon and biomarker concentration records exhibited similar variability,
implying a forcing mechanism that affected input and/or preservation of both marine and
terrestrial organic matter, such as large-scale climate change. Organic carbon and
biomarker abundances then systematically increased throughout the Holocene and
exhibited higher frequency variability, suggesting overall enhanced productivity from
rapidly evolving planktonic communities. Similar patterns of variability between
bacterial hopanol, sterol degradation product, and primary productivity biomarker records
suggest that the productivity biomarkers are recording sea surface and water column
processes, and are not significantly biased by sedimentary diagenesis. Low bound sulfur
content in lipid extracts and a lack of observed sulfur-containing compounds argue
against significant sulfurization and resultant biomarker sequestration in 1228D
sediments. Factor analysis provided a statistical means of separating terrestrial and
marine organic inputs, and reinforced the interpretations that very long chain n-alkanoic
acids (C30-C32) are terrestrially derived and sterol compounds primarily represent marine
algal inputs. In all, the biomarker records suggest millennial-scale changes in upwelling
strength superimposed on longer-term trends, with additional variability in contributions
from specific precursors, such as dinoflagellates. Terrestrial leaf wax compounds also
exhibited high-amplitude, millennial-scale variability, but with a different pattern of
change than the marine inputs. GC/TOF-MS was shown to be a useful tool for
generating high-resolution records of the type necessary to understand the relationships
between biomarkers in a complex and sensitive depositional environment such as the
Peru Margin.
Climate signals embedded in the Peru Margin biomarker records provided clues
as to the productivity and upwelling histories of the Peru Margin, as well as regional
terrestrial vegetation. Elevated concentrations of marine biomarkers suggest enhanced
upwelling and productivity from about 6.5 ka to the present on the Peru Margin, with
lower-amplitude millennial-scale variations occurring throughout this period. Enhanced
dinosterol abundances after 6.5 ka are consistent with greater occurrences and/or strength
of El Niño, while concurrently enhanced upwelling suggests a parallel increase in La
Niña activity. Similar timing of mid to late Holocene variability between Peru Margin
marine biomarker records, a faunal sea surface temperature record from the eastern
tropical Atlantic, and Andean paleoclimate records suggests strong climate links between
these regions of the tropics, likely driven by broad-scale changes in El Niño and the
Southern Oscillation (ENSO) and trade wind strength. The C30 n-alkanoic acid, which is
representative of vascular plant leaf wax inputs, exhibited millennial-scale variability
superimposed on longer-term trends that may be related to aridity, assuming fluvial
transport of terrestrial material. n-Alkanoic acid δ13C is generally enriched during
periods of enhanced leaf wax abundance, consistent with increased inputs of C4 plant
material at these times.Funding for this research was provided by a
Schlanger Ocean Drilling Fellowship, which is part of the NSF-sponsored U.S. Science
Support Program (USSSP). An NSF grant to TIE (OCE-0402533) provided additional
funding for the research presented in Chapters 3-5. Funding for the Cariaco Basin
isotopic analyses was provided by the Frank and Lisina Hoch Endowed Fund and the
Woods Hole Oceanographic Institution Director’s General Discretionary Fund
Reporting, interpretation, and extrapolation issues (SPIN) in abstracts of orthodontic meta-analyses published from 2000 to 2020
Summary
Aim
To assess the prevalence of and identify factors associated with SPIN in abstracts of orthodontic meta-analyses.
Materials and methods
Electronic search was performed within the contents of five orthodontic journals and the Cochrane Database of Systematic Reviews (CDSR) to identify meta-analyses of studies involving humans, from 1 January 2000 until 31 August 2020. Inclusion of SPIN in the abstract of meta-analyses, defined as misleading reporting, misleading interpretation, and inappropriate extrapolation of the findings, was documented. Extent of SPIN and associations with journal and year of publication, type of study, number of authors, continent of authorship, methodologist involvement, funding, and significance of the primary outcome were investigated.
Results
One hundred and nine meta-analyses were identified, with the highest proportion being published in the European Journal of Orthodontics (EJO: 31/109; 28.4%). Inclusion of SPIN, in at least one domain, was recorded in nearly half (53/109; 48.6%) of the studies, of which 30 (56.6%) included 2 or more domains of SPIN. Meta-analyses of observational studies presented 1.66 times higher risk for including SPIN in their abstracts compared with interventional ones [95% confidence intervals (CIs): 1.14, 2.40; P = 0.007], after adjusting for a number of predictors. Studies with a large number of authors (≥6) presented 1.76 times higher risk of SPIN (≥6 versus 1–3: 95% CIs: 1.04, 2.97; Wald test, P = 0.021), conditional on the pre-defined predictors.
Conclusions
Flaws in the reporting and interpretation of the findings of abstracts of meta-analyses, as framed by inclusion of SPIN are persistent in orthodontic research, being more prevalent in meta-analyses of observational studies. Consistent, multidirectional efforts should be endorsed to improve the quality of the disseminated research findings
Architecture of the central region of factor H and its interaction with PspC of S. pneumoniae
The complement system is a major component of innate immunity and an effector of
antibody-mediated immune responses. Unlike the other two activation pathways of
the complement system, the alternative pathway is permanently switched on.
Discrimination by complement between self and foreign is therefore achieved by
selective protection of healthy host tissue and cells.
This study investigated the alternative pathway regulator factor H (FH),
which is crucial for protection of self surfaces from complement. FH engages via its
N- and C- terminal ends with activation-specific fragments of C3, C3b and C3d. The
middle region of FH has no binding sites for complement components. It presumably
ensures that the binding sites at either end of the extended and flexible FH molecule
cooperate in recognizing C3b in fluid phase or on self surfaces, but not on foreign
targets.
This study was aimed at achieving an atomic level understanding of the
structure of the middle portion of FH, thereby testing hypotheses as to how it
promotes the overall biological efficacy of the intact protein. High-resolution NMR-derived
structures of two module pairs FH-10-11 and FH-11-12 were solved and
combined with SAXS data to produce a model of FH-10-12. This was combined, in
silico, with the previously solved FH-12-13 structure, then the model of FH-10-13
was used to revisit SAXS data for FH-10-15 and FH-8-15. A unique structure
emerged, unlike any other encountered previously in the family of complement
regulators, in which CCPs 13, 14 and 15 have a highly compacted organization that
has repercussions for function.
While devoid of binding affinity for host ligands, this central region is a
binding site for PspC, a virulence factor of S. pneumoniae. It has been speculated that
the bacteria use this interaction to sequester FH in a conformation that resembles the
one adopted by FH on self cells and makes it particularly good at regulating
complement. Structural and functional investigations of this interaction were
performed to establish the molecular basis of the use of FH by this pathogen in order
to avoid complement-mediated elimination. It was found that PspC and FH form a
near-irreversible complex, while FH-8-15 binds PspC almost as tightly as intact
protein. When bound to PspC, FH has a higher affinity for some of its targets,
supporting the theory that this bacterial protein stabiles a particularly active
conformation of the regulator
New Integrated Waveguides Concept and Development of Substrate Integrated Antennas with Controlled Boundary Conditions
The unprecedented development of substrate integrated circuits (SICs) has made a widespread necessity for further studies and development of waveguides and antennas based on this technology. As the operating frequency is on the rise, the conventional designs of the substrate integrated components are becoming more problematic and costly. Therefore, some techniques are proposed to improve the performance of the waveguides and antennas based on the concept of substrate integrated technology.
First, the problems of the recently developed ridge gap waveguide (RGW) are resolved by introducing a new configuration of this technology which has considerable advantages over the original version of the RGW regarding its construction technology, propagation mode, characteristic impedance, and insertion loss. Second, the configuration of substrate integrated waveguide (SIW), which has been widely accepted for planar and integrated microwave circuits, is modified to operate with low insertion loss at high frequencies without bearing the anisotropic nature of the dielectric material.
The substrate integrated antennas have a strong potential to be used in the compact wireless devices as they can be easily integrated with the baseband circuits. In the horn family, the H-plane horn antenna that can be implemented in the integrated form has received considerable attention in recent years. However, numerous problems are associated with this antenna such as limited bandwidth, tapered aperture distribution, high back radiation, and E-plane asymmetry. Several new techniques are introduced to improve the performance of this antenna, especially at millimeter wave frequencies
Το παιχνίδι στα σχολικά αναγνώσματα και στο πολιτισμικό προϊόν για παιδιά στη σύγχρονη Ελλάδα
ΠΕΡΙΛΗΨΗ
Η ανάγκη του ανθρώπου για παιχνίδι παραμένει αναλλοίωτη στο πέρασμα των
αιώνων. Παίζει σημαντικό ρόλο σε πολλές εκφάνσεις της ζωής του ανθρώπου, ενώ,
αποτελεί βασική δραστηριότητα των παιδιών. Συμβάλλει στην πολύπλευρη εξέλιξή
του καθώς επηρεάζει τη γνωστική, συναισθηματική, κοινωνική αλλά και σωματική
ανάπτυξή του. Το θεατρικό παιχνίδι, με τη σειρά του, ενώνει τον κόσμο του θεάτρου
και του παιχνιδιού, ενθαρρύνοντας την ανάπτυξη ικανοτήτων και δεξιοτήτων. Τα
σχολικά εγχειρίδια κατέχοντας πρωτεύοντα ρόλο στη διδασκαλία, αποτελούν μέσα
που διαδραματίζουν σπουδαίο ρόλο στην κοινωνικοποίηση των μαθητών/τριών.
Συνδυάζοντας τις παραπάνω γνώσεις, τη σπουδαιότητα κάθε παράγοντα χωριστά,
αλλά και τη σύνδεση που υπάρχει μεταξύ τους παρουσιάζουμε τα ευρήματα για την
ύπαρξη παιγνιωδών δραστηριοτήτων στα σχολικά εγχειρίδια της Γλώσσας και των
Μαθηματικών της Α’ Δημοτικού.ABSTRACT
Man's need for play remains unchanged over the centuries. It plays an
important role in many aspects of human life, while it is a basic activity of children. It
contributes to its multifaceted development as it affects its cognitive, emotional,
social and physical development. Theatrical play, in turn, unites the world of theater
and play, encouraging the development of skills and abilities. School textbooks,
playing a key role in teaching, are tools that play an important role in the socialization
of students. Combining the above knowledge, the importance of each factor
separately and also the connection that exists between them, we present the findings
for the existence of playful activities in the textbooks of Language and Mathematics
of the 1st Primary School
Adhesion of Porphyromonas gingivalis and Biofilm Formation on Different Types of Orthodontic Brackets
Objectives. To examine the interaction between Porphyromonas gingivalis and 3 different orthodontic brackets in vitro, focusing on the effect of an early salivary pellicle and other bacteria on the formation of biofilms. Material and Methods. Mono- and multi-species P. gingivalis biofilms were allowed to form in vitro, on 3 different bracket types (stainless steel, ceramic and plastic) with and without an early salivary pellicle. The brackets were anaerobically incubated for 3 days in Brain Heart Infusion Broth to form biofilms. Bacteria were quantified by trypsin treatment and enumeration of the total viable counts of bacteria recovered. Results. Saliva was found to significantly affect (P < 0.001) adhesion and biofilm formation of P. gingivalis, with higher numbers for the coated brackets. No significant effect was detected for the impact of the type of biofilm, although on stainless steel and plastic brackets there was a tendency for higher numbers of the pathogen in multi-species biofilms. Bracket material alone was not found to affect the number of bacteria. Conclusions. The salivary pellicle seems to facilitate the adhesion of P. gingivalis and biofilm formation on orthodontic brackets, while the material comprising the brackets does not significantly impact on the number of bacteria
High-sensitivity measurement of diverse vascular plant-derived biomarkers in high-altitude ice cores
Author Posting. © American Geophysical Union, 2009. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Geophysical Research Letters 36 (2009): L13501, doi:10.1029/2009GL037643.Semi-volatile organic compounds derived from burned and fresh vascular plant sources and preserved in high-altitude ice fields were detected and identified through use of recently developed analytical tools. Specifically, stir bar sorptive extraction and thermal desorption coupled with gas chromatography/time-of-flight mass spectrometry allowed measurement of multiple biomarkers in small sample volumes (≤30 ml). Among other compounds of interest, several diterpenoids, which suggest inputs from conifers and conifer burning, were identified in post-industrial era and older Holocene ice from the Sajama site in the Bolivian Andes, but not in a glacial period sample, consistent with aridity changes. Differences in biomarker assemblages between sites support the use of these compounds as regionally constrained recorders of vegetation and climate change. This study represents the first application of these analytical techniques to ice core research and the first indication that records of vegetation fires may be reconstructed from diterpenoids in ice.This
project was supported in part by NSF-OCE (0402533), and NSF-EAR
(0094475)
Torque expression of 0.018 and 0.022 inch conventional brackets
The aim of this study was to assess the effect of the moments generated with low- and high-torque brackets. Four different bracket prescription-slot combinations of the same bracket type (Mini Diamond® Twin) were evaluated: high-torque 0.018 and 0.022 inch and low-torque 0.018 and 0.022 inch. These brackets were bonded on identical maxillary acrylic resin models with levelled and aligned teeth and each model was mounted on the orthodontic measurement and simulation system (OMSS). Ten specimens of 0.017×0.025 inch and ten 0.019×0.025 inch stainless steel archwires (ORMCO) were evaluated in the low- and high-torque 0.018 inch and 0.022 inch brackets, respectively. The wires were ligated with elastomerics into the brackets and each measurement was repeated once after religation. Two-way analysis of variance and t-test were conducted to compare the generated moments between wires at low- and high-torque brackets separately. The maximum moment generated by the 0.017×0.025 inch stainless steel archwire in the 0.018 inch brackets at +15 degrees ranged from 14.33 and 12.95 Nmm for the high- and low-torque brackets, respectively. The measured torque in the 0.022 inch brackets with the 0.019×0.025 inch stainless steel archwire was 9.32 and 6.48 Nmm, respectively. The recorded differences of maximum moments between the high- and low-torque series were statistically significant. High-torque brackets produced higher moments compared with low-torque brackets. Additionally, in both high- and low-torque configurations, the thicker 0.019×0.025 inch steel archwire in the 0.022 inch slot system generated lower moments in comparison with the 0.017×0.025 inch steel archwire in the 0.018 inch slot syste
A comparative assessment of torque generated by lingual and conventional brackets
The aim of this study was to assess the effect of bracket type on the labiopalatal moments generated by lingual and conventional brackets. Incognito™ lingual brackets (3M Unitek), STb™ lingual brackets (Light Lingual System; ORMCO), In-Ovation L lingual brackets (DENTSPLY GAC), and conventional 0.018 inch slot brackets (Gemini; 3M Unitek) were bonded on identical maxillary acrylic resin models with levelled and aligned teeth. Each model was mounted on the orthodontic measurement and simulation system and 10 0.0175 × 0.0175 TMA wires were used for each bracket type. The wire was ligated with elastomerics into the Incognito, STb, and conventional brackets and each measurement was repeated once after religation. A 15 degrees buccal root torque (+15 degrees) and then a 15 degrees palatal root torque (−15 degrees) were gradually applied to the right central incisor bracket. After each activation, the bracket returned to its initial position and the moments in the sagittal plane were recorded during these rotations of the bracket. One-way analysis of variance with post hoc multiple comparisons (Tukey test at 0.05 error rate) was conducted to assess the effect on bracket type on the generated moments. The magnitude of maximum moment at +15 degrees ranged 8.8, 8.2, 7.1, and 5.8 Nmm for the Incognito, STb, conventional Gemini, and the In-Ovation L brackets, respectively; similar values were recorded at −15 degrees: 8.6, 8.1, 7.0, and 5.7 Nmm, respectively. The recorded differences of maximum moments were statistically significant, except between the Incognito and STb brackets. Additionally, the torque angles were evaluated at which the crown torque fell well below the minimum levels of 5.0 Nmm, as well as the moment/torque ratio at the last part of the activation/deactivation curve, between 10 and 15 degrees. The lowest torque expression was observed at the self-ligating lingual brackets, followed by the conventional brackets. The Incognito and STb lingual brackets generated the highest moment
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