440 research outputs found
Magnetic behavior of nanocrystalline ErCo2
We have investigated the magnetic behavior of the nanocrystalline form of a
well-known Laves phase compound, ErCo2 - the bulk form of which has been known
to undergo an interesting first-order ferrimagnetic ordering near 32 K -
synthesized by high-energy ball-milling. It is found that, in these
nanocrystallites, Co exhibits ferromagnetic order at room temperature as
inferred from the magnetization data. However, the magnetic transition
temperature for Er sublattice remains essentially unaffected as though the
(Er)4f-Co(3d) coupling is weak on Er magnetism. The net magnetic moment as
measured at high fields, sat at 120 kOe, is significantly reduced with respect
to that for the bulk in the ferrimagnetically ordered state and possible
reasons are outlined. We have also compared the magnetocaloric behavior for the
bulk and the nano particles.Comment: JPCM, in pres
Fast computation by block permanents of cumulative distribution functions of order statistics from several populations
The joint cumulative distribution function for order statistics arising from
several different populations is given in terms of the distribution function of
the populations. The computational cost of the formula in the case of two
populations is still exponential in the worst case, but it is a dramatic
improvement compared to the general formula by Bapat and Beg. In the case when
only the joint distribution function of a subset of the order statistics of
fixed size is needed, the complexity is polynomial, for the case of two
populations.Comment: 21 pages, 3 figure
Penning Spectroscopy and Structure of Acetylene Oligomers in He Nanodroplets
Embedded atoms or molecules in a photoexcited He nanodroplet are well-known
to be ionized through inter-atomic relaxation in a Penning process. In this
work, we investigate the Penning ionization of acetylene oligomers occurring
from the photoexcitation bands of He nanodroplets. In close analogy to
conventional Penning electron spectroscopy by thermal atomic collisions, the n
= 2 photoexcitation band plays the role of the metastable atomic
He. This facilitates electron spectroscopy of acetylene
aggregates in the sub-kelvin He environment, providing the following insight
into their structure: The molecules in the dopant cluster are loosely bound van
der Waals complexes rather than forming covalent compounds. In addition, this
work reveals a Penning process stemming from the n = 4 band where
charge-transfer from autoionized He in the droplets is known to be the dominant
relaxation channel. This allows for excited states of the remnant dopant
oligomer Penning-ions to be studied. Hence, we demonstrate Penning ionization
electron spectroscopy of doped droplets as an effective technique for
investigating dopant oligomers which are easily formed by attachment to the
host cluster.Comment: 22 pages, 1 png figure, 4 postscript figure
Null cone preserving maps, causal tensors and algebraic Rainich theory
A rank-n tensor on a Lorentzian manifold V whose contraction with n arbitrary
causal future directed vectors is non-negative is said to have the dominant
property. These tensors, up to sign, are called causal tensors, and we
determine their general properties in dimension N. We prove that rank-2 tensors
which map the null cone on itself are causal. It is known that, to any tensor A
on V there is a corresponding ``superenergy'' (s-e) tensor T{A} which always
has the dominant property. We prove that, conversely, any symmetric rank-2
tensor with the dominant property can be written in a canonical way as a sum of
N s-e tensors of simple forms. We show that the square of any rank-2 s-e tensor
is proportional to the metric if N<5, and that this holds for the s-e tensor of
any simple form for arbitrary N. Conversely, we prove that any symmetric rank-2
tensor T whose square is proportional to the metric must be, up to sign, the
s-e of a simple p-form, and that the trace of T determines the rank p of the
form. This generalises, both with respect to N and the rank p, the classical
algebraic Rainich conditions, which are necessary and sufficient conditions for
a metric to originate in some physical field, and has a geometric
interpretation: the set of s-e tensors of simple forms is precisely the set of
tensors which preserve the null cone and its time orientation. It also means
that all involutory Lorentz transformations (LT) can be represented as s-e
tensors of simple forms, and that any rank-2 s-e tensor is the sum of at most N
conformally involutory LT. Non-symmetric null cone preserving maps are shown to
have a causal symmetric part and are classified according to the null
eigenvectors of the skew-symmetric part. We thus obtain a complete
classification of all conformal LT and singular null cone preserving maps on V.Comment: 36 pages, no figures, LaTeX fil
A rigid barrier between the heart and sternum protects the heart and lungs against rupture during negative pressure wound therapy
<p>Abstract</p> <p>Objectives</p> <p>Right ventricular heart rupture is a devastating complication associated with negative pressure wound therapy (NPWT) in cardiac surgery. The use of a rigid barrier has been suggested to offer protection against this lethal complication, by preventing the heart from being drawn up and damaged by the sharp edges of the sternum. The aim of the present study was to investigate whether a rigid barrier protects the heart and lungs against injury during NPWT.</p> <p>Methods</p> <p>Sixteen pigs underwent median sternotomy followed by NPWT at -120 mmHg for 24 hours, in the absence (eight pigs) or presence (eight pigs) of a rigid plastic disc between the heart and the sternal edges. The macroscopic appearance of the heart and lungs was inspected after 12 and 24 hours of NPWT.</p> <p>Results</p> <p>After 24 hours of NPWT at -120 mmHg the area of epicardial petechial bleeding was 11.90 ± 1.10 cm<sup>2 </sup>when no protective disc was used, and 1.15 ± 0.19 cm<sup>2 </sup>when using the disc (p < 0.001). Heart rupture was observed in three of the eight animals treated with NPWT without the disc. Lung rupture was observed in two of the animals, and lung contusion and emphysema were seen in all animals treated with NPWT without the rigid disc. No injury to the heart or lungs was observed in the group of animals treated with NPWT using the rigid disc.</p> <p>Conclusion</p> <p>Inserting a rigid barrier between the heart and the sternum edges offers protection against heart rupture and lung injury during NPWT.</p
Major bleeding during negative pressure wound/V.A.C.® - therapy for postsurgical deep sternal wound infection - a critical appraisal
Negative-pressure wound therapy, commercially known as vacuum-assisted closure (V.A.C.®) therapy, has become one of the most popular (and efficacious) interim (prior to flap reconstruction) or definite methods of managing deep sternal wound infection. Complications such as profuse bleeding, which may occur during negative-pressure therapy but not necessarily due to it, are often attributed to a single factor and reported as such. However, despite the wealth of clinical experience internationally available, information regarding certain simple considerations is still lacking. Garnering information on all the factors that could possibly influence the outcome has become more difficult due to a (fortunate) decrease in the incidence of deep sternal wound infection. If more insight is to be gained from fewer clinical cases, then various potentially confounding factors should be fully disclosed before complications can be attributed to the technique itself or improvements to negative-pressure wound therapy for deep sternal wound infection can be accepted as evidence-based and the guidelines for its use adapted. The authors propose the adoption of a simple checklist in such cases
The concept of negative pressure wound therapy (NPWT) after poststernotomy mediastinitis – a single center experience with 54 patients
Deep sternal infections, also known as poststernotomy mediastinitis, are a rare but often fatal complication in cardiac surgery. They are a cause of increased morbidity and mortality and have a significant socioeconomic aspect concerning the health system. Negative pressure wound therapy (NPWT) followed by muscular pectoralis plasty is a quite new technique for the treatment of mediastinitis after sternotomy. Although it could be demonstrated that this technique is at least as safe and reliable as other techniques for the therapy of deep sternal infections, complications are not absent. We report about our experiences and complications using this therapy in a set of 54 patients out of 3668 patients undergoing cardiac surgery in our institution between January 2005 and April 2007
Plasma synthesis of single crystal silicon nanoparticles for novel electronic device applications
Single-crystal nanoparticles of silicon, several tens of nm in diameter, may
be suitable as building blocks for single-nanoparticle electronic devices.
Previous studies of nanoparticles produced in low-pressure plasmas have
demonstrated the synthesis nanocrystals of 2-10 nm diameter but larger
particles were amorphous or polycrystalline. This work reports the use of a
constricted, filamentary capacitively coupled low-pressure plasma to produce
single-crystal silicon nanoparticles with diameters between 20-80 nm. Particles
are highly oriented with predominant cubic shape. The particle size
distribution is rather monodisperse. Electron microscopy studies confirm that
the nanoparticles are highly oriented diamond-cubic silicon.Comment: accepted for publication in Plasma Physics and Controlled Fusion,
scheduled for Dec. 2004 F
Ascorbic acid pre-treated quartz stimulates TNF-α release in RAW 264.7 murine macrophages through ROS production and membrane lipid peroxidation
<p>Abstract</p> <p>Background</p> <p>Inhalation of crystalline silica induces a pulmonary fibrotic degeneration called silicosis caused by the inability of alveolar macrophages to dissolve the crystalline structure of phagocytosed quartz particles. Ascorbic acid is capable of partially dissolving quartz crystals, leading to an increase of soluble silica concentration and to the generation of new radical sites on the quartz surface. The reaction is specific for the crystalline forms of silica. It has been already demonstrated an increased cytotoxicity and stronger induction of pro-inflammatory cyclooxygenase-2 (COX-2) by ascorbic acid pre-treated quartz (QA) compared to untreated quartz (Q) in the murine macrophage cell line RAW 264.7.</p> <p>Methods</p> <p>Taking advantage of the enhanced macrophage response to QA as compared to Q particles, we investigated the first steps of cell activation and the contribution of early signals generated directly from the plasma membrane to the production of TNF-α, a cytokine that activates both inflammatory and fibrogenic pathways.</p> <p>Results</p> <p>Here we demonstrate that TNF-α mRNA synthesis and protein secretion are significantly increased in RAW 264.7 macrophages challenged with QA as compared to Q particles, and that the enhanced response is due to an increase of intracellular ROS. Plasma membrane-particle contact, in the absence of phagocytosis, is sufficient to trigger TNF-α production through a mechanism involving membrane lipid peroxidation and this appears to be even more detrimental to macrophage survival than particle phagocytosis itself.</p> <p>Conclusion</p> <p>Taken together these data suggest that an impairment of pulmonary macrophage phagocytosis, i.e. in the case of alcoholic subjects, could potentiate lung disease in silica-exposed individuals.</p
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