6,177 research outputs found
Differential AIP activation for precision and whole-hand visually-guided grasping
No full textBackground
Recent neuroimaging evidence suggests that, in humans, special mechanisms are engaged in the planning and execution of grasping movements.
Grasping requires a visuomotor transformation of object properties into a specific motor program, giving the hand a shape suitable to grasp the object: a fundamental role in this process is played by the anterior intraparietal area (AIP), whose selective involvement in grasping but not reaching actions has been demonstrated by several studies (Binkofski, 1998; Culham, 2004).
Thus, experimental evidence seems to converge on the hypothesis of a key role of AIP in the "hand-shaping" process. However, the extent to which different types of grasp are represented in the same or different cortical loci remains matter of debate. To date, no studies have considered the influence of object dimensions - and thus, the type of prehension required- on AIP involvement.
Methods
A functional magnetic resonance imaging study has been conducted. Spherical 3D plastic objects (3 and 6 cm) were presented, requiring either precision grip -thumb-index finger opposition- or whole-hand prehension: participants had to reach or grasp them.
Hypotheses
We hypothesize that the subtraction of the BOLD signal (Blood Oxygenation Level Dependent) detected for reaching trials from that detected for grasping trials should isolate brain areas responsible for the "hand-shaping" process.Vice versa, the subtraction of grasping-related activation from that detected for reaching trials should highlight areas engaged in inhibition of the act of prehension, presumably elicited by the vision of graspable objects (Handy, 2003).
Results
Results indicate that the two kinds of grasping actions are supported by different patterns of brain activations. AIP contribution seems to be significant only for actions requiring high level of precision: while for whole-hand prehension significant BOLD increase is restricted to primary motor cortex (BA 6) and cerebellum, precision grip involves also parietal areas, as the inferior parietal lobule (BA 40) and the post-central gyrus (BA 3).
The opposite contrast (reaching - grasping) underlines contribution of the right inferior frontal gyrus (BA 44, 45) and of the left superior frontal gyrus (BA 6). Increase of activity in these brain regions was detected only for actions performed toward the small object.
Conclusions
Our results are not in a complete agreement with the hypothesis emerging from the literature suggesting AIP as the "grasping area" in humans: its involvement seems to be necessary only when action goal requires high level of precision. Also prehension inhibition seems to be more demanding when occurring toward a small object than toward a bigger object
Taken together, our results suggest the hypothesis of a modulatory role of target dimension on brain activity supporting hand-object interactions
Growth of single-wall carbon nanotubes by chemical vapor deposition for electrical devices
No full textCarbon emerges in di®erent forms. Diamond and graphite have been well known mate-
rials for centuries. Moreover fullerenes and nanotubes were discovered only a few years ago.
H. W. Kroto et al. depicted the fullerenes in 1985 [1]. A few years later, in 1991, S. Iijima
described carbon nanotubes (CNTs) for the ¯rst time [2] (Figure 1.1).
CNTs have a close relation to graphite, since a single-wall carbon nanotube is like a rolled-up
graphite mono layer. However a nanotube has with its curved shape a higher chemical reacti-
vity than a °at graphite layer. Both the side wall and the caps can be modi¯ed chemically [3].
Carbon nanotubes are regular carbon clusters with attractive mechanical and electronic pro-
perties [4]. Nanotubes have a high mechanical strength due to a very large Young's modu-
lus [5]. They can be used for the storage of hydrogen [5, 6], to store energy in electrochemical
double layer capacitors [7] or to reinforce composite materials [3]. A single nanotube can be
used as a sensor [8{12], a nanorelay [13], a vessel [14] or as a template [3, 15]. It is possible
to produce light bulbs [16] and ¯bers [17] with carbon nanotubes. An array of CNTs can act
as a °at panel display [3, 5] using their feature to act as ¯eld emitting devices [18{21].
CNTs are either metallic (1/3) or semiconducting (2/3). Nowadays it is not possible to select
the desired characteristic of a nanotube in advance. It is only possible to separate metallic
from semiconducting tubes by using an electrical ¯eld [22]. Metallic nanotubes with their
diameter of a few nm represent the ultimate conducting wire whereas the semiconducting
ones can be used as transistors [23{25] even on a transparent and °exible substrate [26]. The
transistors can be optimized by the chemical control of the nanotube-electrode interface [27].
Quantum dots [28, 29] and spin valves [30{32] can be built alike simple logic gates [33] and a
Y-junction recti¯er [34].
Carbon nanotubes have a very interesting property: they are "1-dimensional" molecules [35].
This has to be explained in a few words. In general, quantum con¯nement leads to a spacing
of the allowed eigenenergies. Electrons cannot hop into a higher energy level if the thermal
energy is much smaller than this energy di®erence. In a nanotube an electron is con¯ned in the
directions perpendicular to the tube axis. The nanotube becomes a 1-dimensional conductor.
For several years members of our research group are exploring the electrical properties of
this very special conductor. The behavior of carbon nanotubes is investigated with electrical
transport measurements at low temperatures (down to 50 mK) and in high magnetic ¯elds
(up to 10 T).
The raw material for the ¯rst experiments [36{38] were multi-wall carbon nanotubes ob-
tained from L. Forr¶o (Ecole Polytechnique F¶ed¶erale de Lausanne) which were produced using
laser ablation. The multi-wall carbon nanotubes were used to investigate the suppression of
tunnelling [36, 39], multiple Andreev re°ection [28, 37], electrical spin injection [30{32] and
quantum dots [37, 40{43].
The next step was to grow single-wall carbon nanotubes using chemical vapor deposition
(CVD) [8,44{46]. This procedure has the advantage to be faster than an external collaboration
and in addition the growth of the tubes directly on the device makes the samples ready for
use without an additional treatment.
It was veri¯ed that the CVD grown tubes are suitable of for electrical devices [47]. Vibrating
nanotubes [48] and an ambipolar ¯eld-e®ect transistor [23] were studied. Kondo e®ect [49]
and Fano-Resonances [50] were investigated as well.
The latter experiments reveal one common de¯ciency. The grown tubes are often not sepa-
rated but bundled [47] (Figure 6.10). Moreover it is not clear if they are multi- or single-wall
tubes. This means for electronic transport measurements that several tubes are measured si-
multaneously. Thus the tube with the best conductivity dominates the measurement, whereas
the other tubes perturb the measured signal by there presence.
The main focus of this thesis is the development of a growth process of single-wall carbon
nanotubes by using CVD. The aim is to overcome the problem of bundling. The grown
nanotubes have to be free of lattice defects and they need to have good electrode-nanotube
contacts in order to make them suitable for electronic transport measurements. They have
to lay °at, well separated and optimally distributed on SiO2 our standard substrate. On the
one hand the tube density should not be too high since this would increase the probability
of shortcuts between the electrodes due to nanotube-nanotube contacts. On the other hand
it should not be too low since this would make the localization of an appropriate nanotube
much more time consuming (Figure 1.2).
Two ways to achieve this goal were tried. The single-wall nanotubes can be bought, dissolved
in a solvent and spread after cleaning and separation [51{57], as in the thesis [46]. The second
possibility is to grow the tubes directly on the device as presented in this thesis.
Growing carbon nanotubes with CVD is very simple, at least in principle. There are only
a few essential things needed: an oven, a substrate, a catalyst and a carbon feedstock. The
main challenge is to acquire the right knowhow.
The ¯rst step was to build up the CVD system. Afterwards the proper growth conditions
and a simple method to check the demanded properties of the grown tubes had to be found.
Scanning electron microscopy (SEM) is the standard characterization tool used in this thesis.
Transmission electron microscopy (TEM) is a helpful mean in order to show that the tubes
are separated and single-wall, since it allows the investigation of the tubes' internal structure.
Atomic force microscopy (AFM) and Raman spectroscopy are used in addition.
Outline of this thesis
² Chapter 2 gives a short overview with respect to the properties, the growth and the
characterization of carbon nanotubes.
² The oven and the gas system are delineated in Chapter 3. Di®erent carbon feedstocks
were used: ethylene/hydrogen, methane, methane/ethylene and methane/hydrogen.
² The steps towards a suitable catalyst are presented in Chapter 4. Evaporated and
liquid based catalysts were tested. An iron molybdenum alumina catalyst dissolved in
2-propanol provides the best results.
² Chapter 5 gives a comparison of the results obtained utilizing di®erent growth processes,
and describes the formation of amorphous carbon and the oxidation of nanotubes.
² Chapter 6 summarizes experiments on di®erent TEM grids (Au, Cu, Mo, Ni, stainless
steel, Ti, quantifoils) and silicon nitride windows.
² The results from collaborations with other group members are presented in Chapter 7.
These experiments show the good quality of the grown tubes
Characterisation of ATP-Dependent Mur Ligases Involved in the Biogenesis of Cell Wall Peptidoglycan in Mycobacterium tuberculosis
No full textATP-dependent Mur ligases (Mur synthetases) play essential roles in the biosynthesis of cell wall peptidoglycan (PG) as they catalyze the ligation of key amino acid residues to the stem peptide at the expense of ATP hydrolysis, thus representing potential targets for antibacterial drug discovery. In this study we characterized the division/cell wall (dcw) operon and identified a promoter driving the co-transcription of mur synthetases along with key cell division genes such as ftsQ and ftsW. Furthermore, we have extended our previous investigations of MurE to MurC, MurD and MurF synthetases from Mycobacterium tuberculosis. Functional analyses of the pure recombinant enzymes revealed that the presence of divalent cations is an absolute requirement for their activities. We also observed that higher concentrations of ATP and UDP-sugar substrates were inhibitory for the activities of all Mur synthetases suggesting stringent control of the cytoplasmic steps of the peptidoglycan biosynthetic pathway. In line with the previous findings on the regulation of mycobacterial MurD and corynebacterial MurC synthetases via phosphorylation, we found that all of the Mur synthetases interacted with the Ser/Thr protein kinases, PknA and PknB. In addition, we critically analyzed the interaction network of all of the Mur synthetases with proteins involved in cell division and cell wall PG biosynthesis to re-evaluate the importance of these key enzymes as novel therapeutic targets in anti-tubercular drug discovery
Installation of insecticide-treated durable wall lining: evaluation of attachment materials and product durability under field conditions.
No full textBACKGROUND: Insecticide-treated durable wall lining (DL) is a new method of vector control designed to supplement LLINs and overcome two inherent limitations of LLINs and IRS: nightly behavioural compliance and short residual activity, respectively. DL is a deltamethrin-treated polyethylene material, which when used to cover interior house walls, functions as long-lasting IRS. Because the DL concept anticipates minimal upkeep, a primary challenge is how to guarantee correct household installation and in situ longevity for several years. Field trials were undertaken on various wall surfaces in Ghana to identify a logistically feasible, durable and re-usable method for DL wall attachment and to pilot new methods for assessing DL durability. METHODS: Over fifty-five candidate attachment or fixing products, including mechanical fasteners, material anchors and adhesives, were evaluated for their ability to tolerate static loads (simulating long-term installation) and short-term heavy weights (imitating shock damage). Attachment products were also scored using qualitative logistical and feasibility criteria, including ease of preparation, grip of fixing to DL and possibility of re-use. RESULTS: The stress tests provided a standardised, reproducible and reliable system for assessing fixing effectiveness and DL durability, with 64% (14/22) of adhesives and 15% (2/13) of mechanical fasteners failing to meet the minimum requirements of attaching DL to mud walls for set time periods. For most fixings, less outward load (0.2-8.0 kg) was required to detach DL from the wall, compared to downward load (0.2-19.2 kg). Fixings were better able to grip DL onto concrete than clay surfaces. Using a plastic nail cap to increase DL attachment area greatly improved grip and outward load tolerance, more so than varying nail size, length or texture. CONCLUSIONS: Based on a series of systematic stress tests, optimized fixing products for polyethylene DL wall attachment were identified. In parallel, a detailed and adaptable method of DL household installation was developed for routine deployment in malaria endemic areas. These standardized stress tests will form the basis for comparative evaluations of new types of DL textile, which incorporate non-pyrethroid insecticides to control malaria transmitted by resistant mosquito populations
Impact of Yeast Glycosylation Pathway on Cell Integrity and Morphology, Glycosylation, Stefana Petrescu (Ed.), ISBN: 978-953-51-0771-2, InTech, Available from: http://www.intechopen.com/books/glycosylation/impact-of-yeast-glycosylation-pathway-on-cell-integrity-and-morphology
No full textProtein glycosylation is a multi step reaction, well conserved in the eukaryotic cells. In N-glycosylation reactions dolichyl phosphate (DolP) serves as a lipid acceptor of sugar residues forming DolPPGlcNAc2Man9Glc3. Dolichyl phosphate mannose (DolPMan) is also a substrate for protein O-glycosylation, where it serves as a donor of the first mannose to be attached to hydroxyl groups of serine or treonine. DolPMan is also involved in the synthesis of the sugar part of glycosylphosphatidyl inositol anchor in yeast and other eukaryotes. Its remnant structure is responsible for the attachment of a large group of glycoproteins to the glucan polymers of the cell wall . Thus, a functional link could be predicted between the dolichol biosynthetic (mevalonate) pathway and subsequent N-glycosylation and O-mannosylation, cell wall assembly and/or fungus–host interaction. Moreover, on the basis of the data presented in this chapter, it can be assumed that the glycosylation pathway in yeast and fungi offers many levels of regulation, which might influence the final quality and quantity of cell wall glycoproteins and consequently cell surface immunogenicity.
In this work we concentrate on early glycosylation defects, resulting from the impaired synthesis of dolichol (Dol) and dolichyl phosphate (DolP) or DolPP oligosaccharide (DolPPGlcNAc2Man9Glc3) assembly, and their effect on the cell integrity and morphology
MDA-MB-231 cell invasion in the structurally homogeneous matrigel.
No full text<p>(A) The MDA-MB-231 cells attached to the matrigel side surface wall at 0 hours. The red line shows the front of the cell group. (B) MDA-MB-231 cell invasion in the matrigel at 96 hours. The cells and matrigel digestion caused gel shrinkage compared with the cell front at 0 hours. (C) Few cells in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0118058#pone.0118058.g003" target="_blank">Fig. 3B</a> stretched out and exhibited slight invasion into the matrigel, as the white arrows denote, indicating that MDA-MB-231 cells could not invade into the stiff matrigel of 100% concentration.</p
Receiver Windowing Design for Narrowband Interference Mitigation in MB-OFDM UWB System
No full textIn 2005, the WiMedia Alliance working with the European Computer Manufacturers Association (ECMA) announced the establishment of the WiMedia MB-OFDM (Multiband Orthogonal Frequency Division Multiplexing) UWB radio platform as their global UWB standard. It was also chosen as the physical layer (PHY) of high data rate wireless specifications for high speed Wireless USB (W-USB), Bluetooth 3.0 and Wireless High-Definition Media Interface (HDMI). However, due to the low power and wide bandwidth nature of UWB systems, in-band narrowband interference (NBI) may hinder the receiver performance. This thesis presents an analysis of NBI impact on the MB-OFDM system for UWB communication. The intent of our analysis is to provide practical solutions for interference mitigation under different NBI models. In our work, a new receiver windowing for zero padding (ZP) OFDM system is proposed to reduce NBI spreading in the MB-OFDM UWB system. Simulations demonstrate the effectiveness of windowing under different NBI models.Microelectronics & Computer EngineeringElectrical Engineering, Mathematics and Computer Scienc
Altered immunolocalization of FGF23 in murine femora metastasized with human breast carcinoma MDA-MB-231 cells
No full textIntroduction After the onset of bone metastasis, tumor cells appear to modify surrounding microenvironments for their benefit, and particularly, the levels of circulating fibroblast growth factor (FGF) 23 in patients with tumors have been highlighted. Materials and methods We have attempted to verify if human breast carcinoma MDA-MB-231 cells metastasized in the long bone of nu/nu mice would synthesize FGF23. Serum concentrations of calcium, phosphate (Pi) and FGF23 were measured in control nu/nu mice, bone-metastasized mice, and mice with mammary gland injected with MDA-MB-231 cells mimicking primary mammary tumors. Results and conclusions MDA-MB-231 cells revealed intense FGF23 reactivity in metastasized lesions, whereas MDA-MB-231 cells cultured in vitro or when injected into the mammary glands (without bone metastasis) showed weak FGF23 immunoreactivity. Although the bone-metastasized MDA-MB-231 cells abundantly synthesized FGF23, osteocytes adjacent to the FGF23-immunopositive tumors, unlike intact osteocytes, showed no FGF23. Despite significantly elevated serum FGF23 levels in bone-metastasized mice, there was no significant decrease in the serum Pi concentration when compared with the intact mice and mice with a mass of MDA-MB-231 cells in mammary glands. The metastasized femora showed increased expression and FGFR1 immunoreactivity in fibroblastic stromal cells, whereas femora of control mice showed no obvious FGFR1 immunoreactivity. Taken together, it seems likely that MDA-MB-231 cells synthesize FGF23 when metastasized to a bone, and thus affect FGFR1-positive stromal cells in the metastasized tumor nest in a paracrine manner
ASIC FFT processor for MB-OFDM UWB system
No full textThe physical layer (PHY) standard of Multi-band Orthogonal Frequency Division Multiplexing (MB-OFDM) Ultra Wideband (UWB) system was defined by ECMA International. In this standard, the data sampling rate from the analog-to-digital converter to the physical layer is up to 528 Msample/s. Therefore, it is a challenge to realize the physical layer of the UWB system-especially the components with high computational complexity in Very Large Scale Integration (VLSI) implementation. Fast Fourier Transform (FFT) block is one of these components. FFT plays an important role in Multi-band OFDM UWB system, which is the demodulation block of OFDM signals. The purpose of this project is to design an Application Specific Integrated Circuit (ASIC) FFT solution for this system. The specification is defined from the system analysis and literature research. All the design choices and considerations are concluded and explained.Based on the algorithm and architecture analysis, a novel Radix22Parallel processor is proposed, which is a small-area and low-power-consumption solution for MB-OFDM UWB system. Both Field Programmable Gate Array (FPGA) and ASIC targeted synthesis results of this architecture are presented.Electrical Engineering, Mathematics and Computer Scienc
- …
