4,017 research outputs found
Multiphoton Ionization of Uracil at 355 nm
We present the experimental results from ionization and dissociation by multiphoton absorption (MPI) of uracil and a mixture of uracil with Ar using a Reflectron time of flight spectrometer along with radiation from 355 nm at pulsed Nd:YAG laser . We focus on the light ions production. The MPI mass spectra show that the presence and intensity of the resulting ions depend on the density power of the laser. The resulting ions in the mass spectra are identified and found similar behavior in the case of H+ and C+ as when multiple charged ions are used. Different results were found in contrast with those, recently reported, when electrons or photons of other wavelength were used. The number of 355nm absorbed photons was calculated accordingly to Keldysh theory and similar results were fond using pure uracil or uracil-Ar mixture. Our results are compared with those obtained in other laboratories under different experimental conditions, some of them show only partial agreement and differences are discussed
Measurement driven quantum evolution
We study the problem of mapping an unknown mixed quantum state onto a known
pure state without the use of unitary transformations. This is achieved with
the help of sequential measurements of two non-commuting observables only. We
show that the overall success probability is maximized in the case of measuring
two observables whose eigenstates define mutually unbiased bases. We find that
for this optimal case the success probability quickly converges to unity as the
number of measurement processes increases and that it is almost independent of
the initial state. In particular, we show that to guarantee a success
probability close to one the number of consecutive measurements must be larger
than the dimension of the Hilbert space. We connect these results to quantum
copying, quantum deleting and entanglement generation.Comment: 7 pages, 1 figur
Fs-detr: Few-shot detection transformer with prompting and without re-training
This paper is on Few-Shot Object Detection (FSOD),
where given a few templates (examples) depicting a novel
class (not seen during training), the goal is to detect all
of its occurrences within a set of images. From a practical perspective, an FSOD system must fulfil the following
desiderata: (a) it must be used as is, without requiring any
fine-tuning at test time, (b) it must be able to process an arbitrary number of novel objects concurrently while supporting
an arbitrary number of examples from each class and (c) it
must achieve accuracy comparable to a closed system. Towards satisfying (a)-(c), in this work, we make the following
contributions: We introduce, for the first time, a simple, yet
powerful, few-shot detection transformer (FS-DETR) based
on visual prompting that can address both desiderata (a) and
(b). Our system builds upon the DETR framework, extending it based on two key ideas: (1) feed the provided visual
templates of the novel classes as visual prompts during test
time, and (2) “stamp” these prompts with pseudo-class embeddings (akin to soft prompting), which are then predicted
at the output of the decoder. Importantly, we show that
our system is not only more flexible than existing methods,
but also, it makes a step towards satisfying desideratum (c).
Specifically, it is significantly more accurate than all methods that do not require fine-tuning and even matches and
outperforms the current state-of-the-art fine-tuning based
methods on the most well-established benchmarks (PASCAL
VOC & MSCOCO)
Evaluation of physical and chemical soil properties under different management types in the south-western Colombian Andes
Aim of study: Evaluating the variability of physical and chemical soil properties under different soil uses in an experimental farmland of the southwestern Colombian Andes.Area of study: This research was conducted at the Botana Experimental Farm in the mountainous area of Nariño, at the south-western Colombia.Material and methods: nine soil variables were measured under six soil uses which included traditional agriculture, agroforestry systems, and a 67-year-old secondary forest that was used as a reference for comparisons with other soil uses. Data was analyzed through Principal Component Analysis and Duncan’s tests.Main results: organic carbon, cation exchange capacity, clay contents and base saturation were the variables with higher variability among soil uses. The secondary forest and an agroforestry system with alley-cropped wax laurel showed the best soil conditions, whilst pastures and monoculture potato crop plots showed the least desirable conditions for all variables.Research highlights: We found that soils under alley-crop with wax laurel presented the characteristics most similar to the secondary forest. Conversely, soils under alley-crop with alder resembled the soils under intensive management (pasture and potato monocrop); which is related to the inadequate management of this agroforestry systems, provoking that the woody component does not accomplish its goal when implemented.Keywords: soil; agroforestry systems; Andes; forest.Abbreviations used: ACAL, Alley cropping of Alder Trees, ACWL; Alley cropping of Wax Laurel; AFS, agroforestry systems; AWC, available water capacity; BD, Bulk Density; BS, Base saturation; CEC, Cation Exchange Capacity; CLA, Clay; CI, Confidence Intervals, INF, Infiltration; ANOVA, Analysis of Variance; OC, Soil Organic Carbon; PAST, Pasture; PCA, Principal Component Analysis; PC, Principal Component; POCR, Potato Crop; POR, Soil Porosity; SCAL, Scattered Alder Trees; SEFO, Secondary Forest; SU, soil uses; AU, Animal unit
Intercellular Trafficking of Gold Nanostars in Uveal Melanoma Cells for Plasmonic Photothermal Therapy
Efficient plasmonic photothermal therapies (PPTTs) using non-harmful pulse laser irradiation at the near-infrared (NIR) are a highly sought goal in nanomedicine. These therapies rely on the use of plasmonic nanostructures to kill cancer cells while minimizing the applied laser power density. Cancer cells have an unsettled capacity to uptake, retain, release, and re-uptake gold nanoparticles, thus offering enormous versatility for research. In this work, we have studied such cell capabilities for nanoparticle trafficking and its impact on the effect of photothermal treatments. As our model system, we chose uveal (eye) melanoma cells, since laser-assisted eye surgery is routinely used to treat glaucoma and cataracts, or vision correction in refractive surgery. As nanostructure, we selected gold nanostars (Au NSs) due to their high photothermal efficiency at the near-infrared (NIR) region of the electromagnetic spectrum. We first investigated the photothermal effect on the basis of the dilution of Au NSs induced by cell division. Using this approach, we obtained high PPTT efficiency after several cell division cycles at an initial low Au NS concentration (pM regime). Subsequently, we evaluated the photothermal effect on account of cell division upon mixing Au NS-loaded and non-loaded cells. Upon such mixing, we observed trafficking of Au NSs between loaded and non-loaded cells, thus achieving effective PPTT after several division cycles under low irradiation conditions (below the maximum permissible exposure threshold of skin). Our study reveals the ability of uveal melanoma cells to release and re-uptake Au NSs that maintain their plasmonic photothermal properties throughout several cell division cycles and re-uptake. This approach may be readily extrapolated to real tissue and even to treat in situ the eye tumor itself. We believe that our method can potentially be used as co-therapy to disperse plasmonic gold nanostructures across affected tissues, thus increasing the effectiveness of classic PPTT
Chemical composition, in vitro cytotoxic and antioxidant activities of the essential oil of Peruvian Minthostachys mollis Griseb
The composition of the essential oil obtained by hydrodistillation from Minthostachys mollis Griseb (Lamiaceae) aerial parts was determined by GC and GC/MS. Menthone (13.2%), pulegone (12.4%), cis-dihydrocarvone (9.8%) and carvacrol acetate (8.8%) were the main essential oil components. The cytotoxic activity of the essential oil was in vitro measured using the MTT colorimetric assay. IC50values were calculated on healthy non-tumor cells (HEK-293) and three human cancer cell lines (T24, DU-145 and MCF-7). In such latter cells, the estimated values were around 0.2 mg/mL. In addition, the antioxidant activity was determined by interaction with the stable freeradical 2,2”-diphenyl-1-picrylhydrazyl. The essential oil was almost devoid of antioxidant activity indicating that its anti-proliferative action relies on other unknown mechanism
Scalar meson dynamics in Chiral Perturbation Theory
A comparison of the linear sigma model (LM) and Chiral Perturbation
Theory (ChPT) predictions for pion and kaon dynamics is presented. Lowest and
next-to-leading order terms in the ChPT amplitudes are reproduced if one
restricts to scalar resonance exchange. Some low energy constants of the order
ChPT Lagrangian are fixed in terms of scalar meson masses. Present values
of these low energy constants are compatible with the LM dynamics. We
conclude that more accurate values would be most useful either to falsify the
LM or to show its capability to shed some light on the controversial
scalar physics.Comment: 9 pages, REVTeX 4.0. Final version accepted for publicatio
The sensitivity of LaBr3:Ce scintillation detectors to low energy neutrons: Measurement and Monte Carlo simulation
AbstractThe neutron sensitivity of a cylindrical ⊘1.5in.×1.5in. LaBr3:Ce scintillation detector was measured using quasi-monoenergetic neutron beams in the energy range from 40keV to 2.5MeV. In this energy range the detector is sensitive to γ-rays generated in neutron inelastic and capture processes. The experimental energy response was compared with Monte Carlo simulations performed with the Geant4 simulation toolkit using the so-called High Precision Neutron Models. These models rely on relevant information stored in evaluated nuclear data libraries. The performance of the Geant4 Neutron Data Library as well as several standard nuclear data libraries was investigated. In the latter case this was made possible by the use of a conversion tool that allowed the direct use of the data from other libraries in Geant4. Overall it was found that there was good agreement with experiment for some of the neutron data bases like ENDF/B-VII.0 or JENDL-3.3 but not with the others such as ENDF/B-VI.8 or JEFF-3.1
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