423 research outputs found
Social Justice in the EU and OECD. Bertelsmann Stiftung Index Report 2019
With the onset of the economic and financial crisis, social justice has deteriorated
â on average â in the OECD and EU countries surveyed by the SJI.1 While the Social
Justice Index shows a slight but ongoing upward trend since economic recovery
began in 2014, the overall score remains below the pre-crisis level. In addition,
there are still striking discrepancies with regard to available opportunities to participate
in society in the 41 countries surveyed
Interaction Of Hydrogen With A Pd(210)- And A Ni(210) Surface
Titelseite und Inhaltsverzeichnis
0\. Einleitung 5
1\. Allgemeiner Teil 7
1.2. Die (210)-OberflÀche 7
1.2. Allgemeines zur H-Adsorption 10
1.3. Dissoziation von Wasserstoff auf MetalloberflÀchen 13
1.4. Zur Bindung von WasserstoffmolekĂŒlen an MetalloberflĂ€chen 23
1.5. Beispiele fĂŒr molekularen Wasserstoff auf MetalloberflĂ€chen 30
2\. Experimenteller Teil 35
2.1. Augerelektronenspektroskopie (AES) 35
2.3. Beugung langsamer Elektronen (LEED) 37
2.3. Thermodesorptionsspektroskopie (TDS) 40
2.4. Ănderung der Austrittsarbeit 44
2.5. Photoemissionsspektroskopie (UPS) 47
2.6. Schwingungsspektroskopie (HREELS) 53
2.7. Apparativer Aufbau 60
2.8. Substrate 63
2.9. ProbenprÀparation 65
Motivation 67
3\. Untersuchungen der reinen Wasserstoffsysteme H2/Pd(210) und H2/Ni(210) 69
3.1. Wechselwirkung von Wasserstoff mit einer Pd(210)-OberflÀche 69
3.2. Wechselwirkung von Wasserstoff mit einer Ni(210)-OberflÀche 86
4\. Zur konkurrierenden Adsorption von atomaren und molekularen Wasserstoff
101
5\. Untersuchungen zum Subsurface-Zustand 118
6\. Das H2/CO/Pd(210)-Koadsorptionssystem 130
6.1. Das reine CO/Pd(210)-System 131
6.2. Die H/CO Koadsorption auf der Pd(210)-OberflÀche 138
6.3. Diskussion 144
7\. Diskussion 150
8.1. Zusammenfassung 167
8.2. Summary 169
9\. Literatur 1718
In der vorliegenden Arbeit wurde die Wechselwirkung von Wasserstoff mit einer
Pd(210)- und Ni(210)-OberflÀche mit Hilfe von Thermodesorptionsspektren (TDS),
Messungen der AustrittsarbeitsÀnderung (DF), Photoemissionsspektren (UPS),
Elektronenenergieverlustspektren (HREELS) und H2/D2-Isotopenaustausch-
Messungen untersucht.
Das H2-Adsorptionsverhalten stimmt fĂŒr beide OberflĂ€chen stark ĂŒberein:
Bei Temperaturen gröĂer als 100K adsorbiert Wasserstoff spontan dissoziativ
und bildet unter Erhöhung der Austrittsarbeit drei atomare BindungszustÀnde.
Wird die Adsorptionstemperatur auf 50K reduziert, adsorbiert der Wasserstoff
zusÀtzlich molekular in zwei ChemisorptionszustÀnde. Dabei wird die
Austrittsarbeit vermindert. Die molekulare Natur dieser ZustÀnde wurde mit
Hilfe von H2/D2-Austauschexperimenten, durch die Beobachtung einer
H-H-Schwingungsbande im HREELS und der Detektion von s-H2/Pd- bzw. s*-H2/Pd-
BindungszustÀnden im UPS belegt. Neben den relativ hohen
Desorptionstemperaturen weist auch die energetische Lage der Signale in den
HREEL- und UP-Spektren eine chemisorptive Wechselwirkung nach. Die in den UP-
Spektren beobachtete H2-induzierte Ănderung der d-Bandstruktur kann mit einem
Bindungsmodell entsprechend dem s-Hin/p-RĂŒckbindungs-Synergismus nach Dewar-
Chatt-Duncanson bzw. Blyholder erklÀrt werden.
Die Beobachtung von chemisorbierten H2-MolekĂŒlen auf einer ĂbergangsoberflĂ€che
ist ungewöhnlich. Nach dem Harris-Andersson-Modell sollte auf
Ăbergangsmetallen die Dissoziation spontan erfolgen, auf Edelmetallen hingegen
inhibiert sein. Hier können bei Temperaturen kleiner als 10K molekular
physisorbierter Wasserstoff stabilisiert werden. Das heiĂt, es besteht nur
eine schwache Van-der-Waals-Wechselwirkung zwischen MolekĂŒl und OberflĂ€che.
Das einzige weitere Beispiel von molekular chemisorbiertem Wasserstoff auf
einer ĂbergangsmetalloberflĂ€che ist das von A.-S. MĂ„rtensson untersuchte
H2/Ni(510)-System. Ist diese gestuften Ni(110)-OberflÀche mit atomarem
Wasserstoff gesÀttigt, adsorbiert weiterer Wasserstoff molekular an den
Stufen. Aus HREELS-Daten ergibt sich eine on top Adsorption.
Wir machen Àhnliche Beobachtungen: WÀhrend die atomare Adsorption auf der
Pd(210)- bzw. Ni(210)-OberflÀche in hochkoordinierte PlÀtze erfolgt,
adsorbiert das MolekĂŒl on top auf Substratatomen der ersten Lage. DF\- und TD-
Experimente deuten darauf hin, daà zur Stabilisierung der molekularen ZustÀnde
eine partielle atomare Vorbelegung der OberflÀche notwendig ist. Mit Hilfe des
in einer Kooperation mit einer Theoretischen Gruppe (A. GroĂ an der TU
MĂŒnchen) entwickelten Adsorptionsmodells wird den verschiedenen molekularen
Desorptionssignalen derselbe Adsorptionsplatz bei unterschiedlicher atomarer
Vorbedeckung zugeordnet. Der molekulare Adsorptionsplatz on top an den gering
koordinierten Substratatomen der ersten Lage ist gleichzeitig der
Dissoziationsplatz. Ăndert sich aufgrund der benachbarten atomaren Adsorption
von Wasserstoff die d-Bandstruktur und damit die ReaktivitÀt dieser
ausgezeichneten Substratatome, wird der dort gebildete molekulare VorlÀufer-
Zustand stabilisiert.
Die in dieser Arbeit vorgestellten Systeme unterscheiden sich im Hinblick auf
die Besetzung des Subsurface-Zustandes. FĂŒr die Pd(210)-OberflĂ€che wird eine
Absorption von Wasserstoff in oberflÀchennahe ZwischengitterplÀtze beobachtet,
fĂŒr die H2/Ni(210)-OberflĂ€che nicht. Dabei ist mit Besetzung des Subsurface-
Zustandes keine Ănderung der Austrittsarbeit oder die Detektion eines
Schwingungsverlustes im HREELS verbunden. In den TD-Spektren wird der
Absorption ein schmales Niedertemperatur-Signal zugeordnet. Diese Beobachtung
wird mit Hilfe des von Okuyama entwickelten Stamping-Modells diskutiert.
Eine H-Absorption wurde bereits fĂŒr andere offene Pd-OberflĂ€chen ( (110) und
(310) ) beobachtet und gilt als besondere Elementeigenschaft von Palladium. Im
Unterschied zu den Pd(110)- und Pd(310)-OberflÀchen ist zur Absorption in den
Pd(210)-Kristall keine Rekonstruktion nötig. Dies und die Beobachtung der
AbhÀngigkeit der Absorptionsgeschwindigkeit von der ProbenprÀparation ist
AnlaĂ dafĂŒr die Existenz eines zur Absorption notwendigen Strukturensembles
auf der nicht-rekonstruierten Pd(210)-OberflÀche zu diskutieren. Als solches
wird der vierfachkoordinierte Muldenplatz und sein benachbarter
dreifachkoordinierter (111)-Mikrofacettenplatz identifiziert.
Daneben wurde auch die H/CO-Koadsorption auf der Pd(210)-OberflÀche
untersucht. Wenn Wasserstoff prĂ€adsorbiert und anschlieĂend CO dosiert wird,
beobachten wir eine H/CO-Komplexbildung. Dies wird durch die Detektion eines
sogenannten S-Signals im H2-TD-Spektrum und eines nH-O-Schwingungsverlustes im
HREELS belegt. Im Gegensatz zu anderen Koadsorptionssystemen desorbiert der
S-Wasserstoff nicht bei den niedrigeren Temperaturen des Desorptionsbereiches,
sondern simultan mit dem Stabilsten der CO-ZustÀnde. Dies deutet auf eine
ungewöhnlich stabile Komplex-Bildung hin.8
This work presents investigations of the interaction of hydrogen with a
Pd(210) and Ni(210) surface using LEED (low energy electron diffraction),
thermal desorption spectroscopy (TDS), work-function measurements
(DF),vibrational loss measurements (HREELS), and isotope exchange experiments.
The interaction of hydrogen with both surfaces is very similar.
For temperatures above 100K, hydrogen chemisorbs spontaneously forming atoms
in three binding states (b1, b2, b3). The atomic adsorption leads to a work
function increase. If the temperature is reduced to 50K, hydrogen additionally
chemisorbs into two molecular states (g1, g2). In contrast to the
b-adsorption, the population of g-states induces a work-function decrease.
The molecular nature of the g-states was confirmed by observation of the H-H
vibration mode in HREELS, by the detection of the s-H2/Pd- and s*-H2/Pd-
bonding in UPS, and by H2/D2-exchange experiments.
The energy range of the HREELS- and UPS-signals and the relatively high
desorption temperature in TD-spectra verify a real chemisorptive interaction
between molecule and surface. We consider a side-on complex configuration
which allows a s/s*-synergism equivalent to the Blyholder backbonding
mechanism for CO chemisorption or the classical Dewar-Chatt-Duncanson model
for the bonding situation in olefine or other organometallic complexes.
A molecular chemisorption of H2 on a transition metal surface is unusual. In
general, hydrogen adsorbs dissociatively. While on noble metals the
dissociation is hindered by a sizable energy barrier, it occurs spontaneously
on transition metal surfaces. If molecular adsorption states exist, they are
usually very weakly bound in shallow physisorption wells; beyond, it requires
surface temperatures below 20K to stabilize those states.
At Ni(510), molecular chemisorption has been observed at surface temperatures
up to 125K, presumably at the steps, but only after the surface was passivated
with a dense atomic layer.
We made similar observations, namely the coexistence of chemisorbed molecular
and atomic hydrogen on the relatively open Pd(210) and Ni(210) surfaces
although the surfaces were not fully passivated. While the atomic adsorption
takes place in high coordinated sites, the molecule adsorbs on top.
It is very difficult to identify experimentally the exact location and nature
of the hydrogen adsorption states. In order to obtain this microscopic
information, A. GroĂ et al. performed DFT calculations. The results suggest
that the hydrogen molecule is first attracted to the top Pd atoms. At the
clean Pd(210) surface, no stable molecular adsorption state should exist and
the hydrogen molecule dissociates into the higher coordinated sites. Due to
the presence of atomic hydrogen on the surface however, this behavior changed
considerably. The presence of hydrogen atoms leads to a molecular adsorption
state at the top site. That the top site`s reactivity is hardly influenced by
the pre-adsorbed hydrogen atoms can be traced back to the induced change in
the local density of states.
In the case of Pd, we observed the absorption of hydrogen atoms which reside
?close to the surface?. Evidence for such a ?subsurface state? is a low-
temperature thermal desorption feature which cannot be saturated, combined
with a vanishing work function change and negligible vibrational loss
contributions of the respective H state. We discuss our observations using the
stamping model developed by Okuyama.
The hydrogen absorption has already been observed on other open palladium
surfaces and is considered as a specific feature of the element palladium. But
in contrast to other open Pd surfaces, the Pd(210) surface need not to
reconstruct for absorption. Futhermore, the absorption velocity depends on the
preparation of the sample. Both observations give rise to the assumption that
a certain ensemble of substrate atoms necessary for chemisorption exists on
the non-reconstructed Pd(210) surface. We can identify this ensemble as the
four-fold coordinated hollow site and the neighbouring three-fold coordinated
site.
In addition, we examined the H/CO-coadsorption on the Pd(210) surface. If the
Pd crystal was first exposed to hydrogen and then to carbon monoxid, we
observed the formation of H/CO-complexes. This observation was verified by the
detection of a so-called S desorption signal in TDS and by a O-H vibrational
loss in HREELS. In contrast to other coadsorption systems the S-hydrogen does
not desorb in the low temperature area. Rather, hydrogen desorbs
simultaneously with the strongly bound carbon monoxid, indicating an unusually
stable complex
Deciduous enamel 3D microwear texture analysis as an indicator of childhood diet in medieval Canterbury, England
This study conducted the first three dimensional microwear texture analysis of human deciduous teeth to reconstruct the physical properties of medieval childhood diet (age 1-8yrs) at St Gregory's Priory and Cemetery (11th to 16th century AD) in Canterbury, England. Occlusal texture complexity surfaces of maxillary molars from juvenile skeletons (n=44) were examined to assess dietary hardness. Anisotropy values were calculated to reconstruct dietary toughness, as well as jaw movements during chewing. Evidence of weaning was sought, and variation in the physical properties of food was assessed against age and socio-economic status. Results indicate that weaning had already commenced in the youngest children. Diet became tougher from four years of age, and harder from age six. Variation in microwear texture surfaces was related to historical textual evidence that refers to lifestyle developments for these age groups. Diet did not vary with socio-economic status, which differs to previously reported patterns for adults. We conclude, microwear texture analyses can provide a non-destructive tool for revealing subtle aspects of childhood diet in the past
Neural basis of somatosensory target detection independent of uncertainty, relevance, and reports
Research on somatosensory awareness has yielded highly diverse findings with putative neural correlates ranging from activity within somatosensory cortex to activation of widely distributed frontoparietal networks. Divergent results from previous studies may reside in cognitive processes that often coincide with stimulus awareness in experimental settings. To scrutinise the specific relevance of regions implied in the target detection network, we used functional magnetic resonance imaging (n = 27) on a novel somatosensory detection task that explicitly controls for stimulus uncertainty, behavioural relevance, overt reports, and motor responses. Using Bayesian Model Selection, we show that responses reflecting target detection are restricted to secondary somatosensory cortex, whereas activity in insular, cingulate, and motor regions is best explained in terms of stimulus uncertainty and overt reports. Our results emphasise the role of sensory-specific cortex for the emergence of perceptual awareness and dissect the contribution of the frontoparietal network to classical detection tasks
Characterization of Epidermal Wound Healing in a Human Skin Organ Culture Model: Acceleration by Transplanted Keratinocytes1
Few data are available on early regeneration of human epidermis in vivo. We have established a supravital skin organ culture model for epidermal wound healing by setting a central defect (3 mm diameter) in freshly excised skin specimens and culturing under air exposure. Re-epithelialization was followed for up to 7 d by histology and immunohistologic analysis of various markers for differentiation and proliferation. In 12 of 19 cases (63%; 5% fetal calf serum) or six of 21 cases (29%; 2% fetal calf serum), the wounds were re-epithelialized spontaneously after 7 d. After transplantation to the wounds of 1â2 Ă 106 dissociated allogenic cultured epidermal or about 1 Ă 106 autologous outer root sheath keratinocytes, 18 of 21 cases (86%; 5% fetal calf serum) or 17 of 21 cases (81%; 2% fetal calf serum) were healed within the same period. Histologically, early neoepithelium (3 d) was disordered after keratinocyte transplantation, whereas later (7 d) it had gained a more ordered stratification, exhibiting a thin discontinuous granular and a compact horny layer. At this stage, not only hyperproliferative (CK 6) but also, abundantly, maturation-associated cytokeratins (CK 1, CK 10) were detected immunohistochemically. Analyses of regenerated epidermis after transplantation of (i) keratinocytes labeled in vitro with BrdU and (ii) heterosexual keratinocytes by immunohistochemistry and fluorescence in situ hybridization for the Y chromosome, respectively, clearly showed that external keratinocytes are physically integrated into the regenerated epidermis and extendedly contribute to its formation. The data presented here demonstrate improvement and acceleration of epidermal re-epithelialization by transplantation of keratinocytes
Bayesian Sensitivity Analysis of Flight Parameters in a Hard-Landing Analysis Process
A flight parameter sensor simulation model was developed to assess the conservatism of the landing gear component loads calculated using a typical hard-landing analysis process. Conservatism exists due to factors of safety that are incorporated into any hard-landing analysis process to account for uncertainty in the measurement of certain flight parameters. The flight parameter sensor simulation model consists of 1) an aircraft and landing gear dynamic model to determine the âactualâ landing gear loads during a hard landing; 2) an aircraft sensor and data acquisition model to represent the aircraft sensors and flight data recorder systems to investigate the effect of signal processing on the flight parameters; and 3) an automated hard-landing analysis process, representative of that used by airframe and equipment manufacturers, to determine the âsimulatedâ landing gear loads. Using a technique of Bayesian sensitivity analysis, a number of flight parameters are varied in the flight parameter sensor simulation model to gain an understanding of the sensitivity of the difference between actual and simulated loads to the individual flight parameters in symmetric and asymmetric two-point landings. This study shows that the error can be reduced by learning the true value of the following flight parameters: longitudinal tireârunway friction coefficient, aircraft vertical acceleration (related to vertical descent velocity), lateral acceleration (related to lateral velocity), Euler roll angle, mass, center of gravity position, and main landing gear tire type. It was also shown that, due to the modeling techniques used, shock absorber servicing state and tire pressure do not contribute significantly to the error
Gross karyotypic and phenotypic alterations among different progenies of the candida glabrata cbs138/atcc2001 reference strain
Peer reviewedPublisher PD
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