811 research outputs found
New Immobilized Catalytic Systems for Batch and Flow Applications
Durant
el
transcurs
de
la
Tesi,
s’ha
desenvolupat
un
sistema
catalític
per
reaccions
aldòliques
altament
estereoselectives
en
flux
continu
basats
en
una
prolina
immobilitzada
en
una
resina
de
poliestirè.
S’ha
demostrat
la
seva
aplicació
com
a
catalitzador
per
a
la
síntesi
de
diferents
substrats,
i
la
seva
utilització
en
condicions
de
flux
continu
va
permetre
la
preparació
a
mitjana
escala
d’un
conjunt
d’adductes
aldòlics.
A
part,
s’han
preparat
diferents
aminoàcids
primaris
ancorats
en
una
resina
de
poliestirè
i
s’han
utilitzats
com
a
catalitzadors
per
reacciones
enantioselectives
del
tipus
aldòliques
i
Mannich.
De
tots
els
aminoàcids
provats,
el
derivat
de
treonina
és
el
que
va
mostrar
més
eficàcia
per
les
dues
reaccions
esmentades.
A
més,
amb
aquest
catalitzador
es
va
poder
portar
a
terme
una
sèrie
de
reaccions
del
tipus
Mannich
altament
enantioselectives
en
condicions
de
flux
continu.
Es
va
dur
a
terme
eficaçment
la
inserció
de
diòxid
de
carboni
a
oxirans
sota
condicions
suaus
de
reacció
en
presencia
d’un
derivat
del
pirogalol
immobilitzat
en
una
resina
de
poliestirè
altament
reciclable.Durante
el
transcurso
de
la
Tesis,
se
ha
desarrollado
un
sistema
catalítico
para
reacciones
aldólicas
altamente
estereoselectivas
en
flujo
continuo
basados
en
prolina
inmovilizada
en
una
resina
de
poliestireno.
Se
ha
demostrado
su
aplicación
como
catalizador
para
la
síntesis
de
diferentes
substratos,
y
su
utilización
en
condiciones
de
flujo
continuo
permitió
la
preparación
a
mediana
escala
de
un
conjunto
de
aductos
aldólicos.
A
parte,
se
han
preparado
diferentes
aminoácidos
primarios
anclados
en
resinas
de
poliéster
y
se
han
utilizado
como
catalizadores
para
reacciones
enantioselectivas
del
tipo
aldólicas
y
Mannich.
De
todos
los
aminoácidos
provados,
el
derivado
de
treonina
era
el
que
mostró
más
eficacia
para
catalizar
las
dos
reacciones
comentadas.
Además,
con
este
catalizador
se
pudo
llevar
a
cabo
una
serie
de
reacciones
del
tipo
Mannich
altamente
enantioselectivas
en
condiciones
de
flujo
continuo.
Se
llevó
a
cabo
eficazmente
la
inserción
de
dióxido
de
carbono
a
oxiranos
bajo
condiciones
suaves
de
reacción
en
presencia
de
un
derivado
del
pirogalol
inmovilizado
en
una
resina
de
poliestireno
altamente
reciclable.During
the
course
of
this
thesis,
a
catalytic
system
for
highly
stereoselective
aldol
reactions
in
continuous
operation
has
been
developed
based
on
polystyrene-‐
supported
proline.
The
applicability
to
different
substrates
and
the
suitability
of
the
flow
system
for
repeated
reuse
allowing
the
medium
scale
preparation
of
a
series
of
aldol
adducts
under
a
single
set
of
reaction
conditions
has
been
demonstrated.
Furthermore,
different
polystyrene-‐supported
primary
amino
acids
have
been
prepared
and
applied
as
catalysts
for
aldol
and
Mannich
reactions.
Out
of
the
amino
acid
derivatives,
immobilized
threonine
shows
the
best
performance
in
both
reactions.
With
this
catalyst,
a
series
Mannich
reactions
could
be
conducted
under
continuous
flow
conditions.
In
the
presence
of
a
highly
recyclable
polystyrene-‐
supported
pyrogallol
derivative,
the
insertion
of
carbon
dioxide
into
oxiranes
under
mild
conditions
was
accomplished
A Perfect Couple
Henseler, J., Schmidt, H. J., & Redler, J. J. (2023). Design Science and Marketing: A Perfect Couple. Journal of Creating Value. https://doi.org/10.1177/23949643231200703This special issue of the Journal on Creating Value about ‘Creating Value through Design Science’ and the articles therein aim at showcasing how design science research in the field of creating value can look like.publishersversionepub_ahead_of_prin
Nonadiabatic pumping in classical and quantum chaotic scatterers
We study directed transport in periodically forced scattering systems in the
regime of fast and strong driving where the dynamics is mixed to chaotic and
adiabatic approximations do not apply. The model employed is a square potential
well undergoing lateral oscillations, alternatively as two- or single-parameter
driving. Mechanisms of directed transport are analyzed in terms of asymmetric
irregular scattering processes. Quantizing the system in the framework of
Floquet scattering theory, we calculate directed currents on basis of
transmission and reflection probabilities obtained by numerical wavepacket
scattering. We observe classical as well as quantum transport beyond linear
response, manifest in particular in a non-zero current for single-parameter
driving where according to adiabatic theory, it should vanish identically.Comment: 13 pages, 8 figure
Floquet scattering in parametric electron pumps
A Floquet scattering approach to parametric electron pumps is presented and
compared with Brouwer's adiabatic scattering approach [Phys. Rev. B 58, R10135
(1998)] for a simple scattering model with two harmonically oscillating
delta-function barriers. For small strength of oscillating potentials these two
approaches give exactly equivalent results while for large strength, these
clearly deviate from each other. The validity of the adiabatic theory is also
discussed by using the Wigner delay time obtained from the Floquet scattering
matrix.Comment: 10 pages, 7 figure
Small Disks and Semiclassical Resonances
We study the effect on quantum spectra of the existence of small circular
disks in a billiard system. In the limit where the disk radii vanish there is
no effect, however this limit is approached very slowly so that even very small
radii have comparatively large effects. We include diffractive orbits which
scatter off the small disks in the periodic orbit expansion. This situation is
formally similar to edge diffraction except that the disk radii introduce a
length scale in the problem such that for wave lengths smaller than the order
of the disk radius we recover the usual semi-classical approximation; however,
for wave lengths larger than the order of the disk radius there is a
qualitatively different behaviour. We test the theory by successfully
estimating the positions of scattering resonances in geometries consisting of
three and four small disks.Comment: Final published version - some changes in the discussion and the
labels on one figure are correcte
Floquet Formalism of Quantum Pumps
We review Floquet formalism of quantum electron pumps. In the Floquet
formalism the quantum pump is regarded as a time dependent scattering system,
which allows us to go beyond the adiabatic limit. It can be shown that the
well-known adiabatic formula given by Brouwer can be derived from the adiabatic
limit of Floquet formalism. We compare various physical properties of the
quantum pump both in the adiabatic and in the non-adiabatic regime using the
Floquet theory.Comment: Latex2e 16 pages, 6 figures. A review paper to appear in Int. J. Mod.
Phys.
- …