988 research outputs found
Striatal Infarction Elicits Secondary Extrafocal MRI Changes in Ipsilateral Substantia Nigra
Focal ischemia may induce pathological alterations in brain areas distant from
the primary lesion. In animal models, exofocal neuron death in the ipsilateral
midbrain has been described after occlusion of the middle cerebral artery
(MCA). Using sequential magnetic resonance imaging (T2- and diffusion-
weighted) at 3 Tesla, we investigated acute ischemic stroke patients on days
1, 2, 6, 8, and 10 after stroke onset. Sixteen consecutive patients who had
suffered a stroke involving the caudate nucleus and/or putamen of either
hemisphere were recruited into the study. Four additional patients with
strokes sparing the caudate nucleus and putamen but encompassing at least one-
third of the MCA territory served as controls. Ischemic lesions involving
striatal structures resulted in hyperintense lesions in ipsilateral midbrain
that emerged between days 6 and 10 after stroke and were not present on the
initial scans. In contrast, none of the control stroke patients developed
secondary midbrain lesions. Hyperintense lesions in the pyramidal tract or the
brain stem caused by degeneration of the corticospinal tract could be clearly
distinguished from these secondary midbrain gray matter lesions and were
detectable from day 2 after ischemia. Co-registration of high-resolution
images with a digitized anatomic atlas revealed localization of secondary
lesions primarily in the substantia nigra pars compacta. Apparent diffusion
coefficient (ADC) values in the secondary lesions showed a delayed sharp
decline through day 10. Normalization of ADC values was observed at late
measurements. Taken together, our study demonstrates that striatal infarction
elicits delayed degenerative changes in ipsilateral substantia nigra pars
compacta
Four different emissions from a Pt(Bodipy)(PEt3)(2)(S-Pyrene) dyad
The Pt(bodipy)-(mercaptopyrene) dyad BPtSPyr shows four different emissions: intense near-infrared phosphorescence (Φph up to 15%) from a charge-transfer state pyrS˙+-Pt-BDP˙−, additional fluorescence and phosphorescence emissions from the 1ππ* and 3ππ* states of the bodipy ligand at r.t., and phosphorescence from the pyrene 3ππ* and the bodipy 3ππ* states in a glassy matrix at 77 K.publishe
Directing energy transfer in Pt(bodipy)(mercaptopyrene) dyads
We report on the photophysical properties of three dyads that combine a 4,4-difluoro-4-bora-3a,4a-diaza-s-indacene (bodipy, BDP) and a mercaptopyrene (SPyr) dye ligand at a Pt(PEt3)(2) fragment. sigma-Bonding of the dyes to the Pt ion promotes intersystem crossing (ISC) via the external heavy atom effect. The coupling of efficient ISC with charge-transfer from the electron-rich mercaptopyrene to the electron-accepting BDP ligand (PB-CT) gives rise to a multitude of (potentially) emissive states. This culminates in the presence of four different emissions for the mono- and dinuclear complexes BPtSPyr and BPtSPyrSPtB with an unsubstituted BDP ligand and either a terminal 1-mercaptopyrene or a bridging pyrene-1,6-dithiolate ligand. Thus, in fluid solution, near IR emission at 724 nm from the (PB)-P-3-CT state is observed with a quantum yield of up to 15%. Excitation into the BDP-based (1)pi pi* or the pyrene-based (1)pi pi* band additionally trigger fluorescence and phosphorescence emissions from the BDP-centred (1)pi pi* and (3)pi pi* states. In frozen solution, at 77 K, phosphorescence from the pyrene ligand becomes the prominent emission channel, while PB-CT emission is absent. Alkylation of the BDP ligand in KBPtSPyr funnels all excitation energy into fluorescence and phosphorescence emissions from the KBDP ligand. The assignments of the various excited states and the deactivation cascades were probed by absorption and emission spectroscopy, transient absorption spectroscopy, electrochemical and UV/Vis/NIR spectroelectrochemical measurements, and by quantum chemical calculations. Our conclusions are further corroborated with the aid of suitable reference compounds comprising of just one chromophore. All dyads are triplet sensitizers and are able to generate singlet oxygen
Recommended from our members
Macro-level Modeling of the Response of <i>C. elegans</i> Reproduction to Chronic Heat Stress
A major goal of systems biology is to understand how organism-level behavior arises from a myriad of molecular interactions. Often this involves complex sets of rules describing interactions among a large number of components. As an alternative, we have developed a simple, macro-level model to describe how chronic temperature stress affects reproduction in C. elegans. Our approach uses fundamental engineering principles, together with a limited set of experimentally derived facts, and provides quantitatively accurate predictions of performance under a range of physiologically relevant conditions. We generated detailed time-resolved experimental data to evaluate the ability of our model to describe the dynamics of C. elegans reproduction. We find considerable heterogeneity in responses of individual animals to heat stress, which can be understood as modulation of a few processes and may represent a strategy for coping with the ever-changing environment. Our experimental results and model provide quantitative insight into the breakdown of a robust biological system under stress and suggest, surprisingly, that the behavior of complex biological systems may be determined by a small number of key components.</p
AERoS: Assurance of Emergent Behaviour in Autonomous Robotic Swarms
The behaviours of a swarm are not explicitly engineered. Instead, they are an
emergent consequence of the interactions of individual agents with each other
and their environment. This emergent functionality poses a challenge to safety
assurance. The main contribution of this paper is a process for the safety
assurance of emergent behaviour in autonomous robotic swarms called AERoS,
following the guidance on the Assurance of Machine Learning for use in
Autonomous Systems (AMLAS). We explore our proposed process using a case study
centred on a robot swarm operating a public cloakroom.Comment: 12 pages, 11 figure
Using Corticomuscular and Intermuscular Coherence to Assess Cortical Contribution to Ankle Plantar Flexor Activity During Gait
The present study used coherence and directionality analyses to explore whether the motor cortex contributes to plantar flexor muscle activity during the stance phase and push-off phase during gait. Subjects walked on a treadmill, while EEG over the leg motorcortex area and EMG from the medial gastrocnemius and soleus muscles was recorded. Corticomuscular and intermuscular coherence were calculated from pair-wise recordings. Significant EEG-EMG and EMG-EMG coherence in the beta and gamma frequency bands was found throughout the stance phase with the largest coherence towards push-off. Analysis of directionality revealed that EEG activity preceded EMG activity throughout the stance phase until the time of push-off. These findings suggest that the motor cortex contributes to ankle plantar flexor muscle activity and forward propulsion during gait
Soft Gripping: Specifying for Trustworthiness
Soft robotics is an emerging technology in which engineers create flexible
devices for use in a variety of applications. In order to advance the wide
adoption of soft robots, ensuring their trustworthiness is essential; if soft
robots are not trusted, they will not be used to their full potential. In order
to demonstrate trustworthiness, a specification needs to be formulated to
define what is trustworthy. However, even for soft robotic grippers, which is
one of the most mature areas in soft robotics, the soft robotics community has
so far given very little attention to formulating specifications. In this work,
we discuss the importance of developing specifications during development of
soft robotic systems, and present an extensive example specification for a soft
gripper for pick-and-place tasks for grocery items. The proposed specification
covers both functional and non-functional requirements, such as reliability,
safety, adaptability, predictability, ethics, and regulations. We also
highlight the need to promote verifiability as a first-class objective in the
design of a soft gripper.Comment: Updated the Standards subsection of paper. 9 pages, 2 figures, 1
table, 34 reference
Insulating and Conducting Phases of RbC60
Optical measurements were performed on thin films of RbC,
identified by X-ray diffraction as mostly material. The samples were
subjected to various heat treatments, including quenching and slow cooling from
400K. The dramatic increase in the transmission of the quenched samples, and
the relaxation towards the transmission observed in slow cooled samples
provides direct evidence for the existence of a metastable insulating phase.
Slow cooling results in a phase transition between two electrically conducting
phases.Comment: Minor revisions. Submitted to PRB, RevTeX 3.0 file, 2 postscript
figures included, ir_dop
Dynamics of gelling liquids: a short survey
The dynamics of randomly crosslinked liquids is addressed via a Rouse- and a
Zimm-type model with crosslink statistics taken either from bond percolation or
Erdoes-Renyi random graphs. While the Rouse-type model isolates the effects of
the random connectivity on the dynamics of molecular clusters, the Zimm-type
model also accounts for hydrodynamic interactions on a preaveraged level. The
incoherent intermediate scattering function is computed in thermal equilibrium,
its critical behaviour near the sol-gel transition is analysed and related to
the scaling of cluster diffusion constants at the critical point. Second,
non-equilibrium dynamics is studied by looking at stress relaxation in a simple
shear flow. Anomalous stress relaxation and critical rheological properties are
derived. Some of the results contradict long-standing scaling arguments, which
are shown to be flawed by inconsistencies.Comment: 21 pages, 3 figures; Dedicated to Lothar Schaefer on the occasion of
his 60th birthday; Changes: added comments on the gel phase and some
reference
- …