950 research outputs found
An improvement of stochastic gradient descent approach for mean-variance portfolio optimization problem
In this paper, the current variant technique of the stochastic gradient descent (SGD) approach, namely, the adaptive moment
estimation (Adam) approach, is improved by adding the standard error in the updating rule. ,e aim is to fasten the convergence
rate of the Adam algorithm. ,is improvement is termed as Adam with standard error (AdamSE) algorithm. On the other hand,
the mean-variance portfolio optimization model is formulated from the historical data of the rate of return of the S&P 500 stock,
10-year Treasury bond, and money market. ,e application of SGD, Adam, adaptive moment estimation with maximum
(AdaMax), Nesterov-accelerated adaptive moment estimation (Nadam), AMSGrad, and AdamSE algorithms to solve the meanvariance
portfolio optimization problem is further investigated. During the calculation procedure, the iterative solution converges
to the optimal portfolio solution. It is noticed that the AdamSE algorithm has the smallest iteration number. ,e results show that
the rate of convergence of the Adam algorithm is significantly enhanced by using the AdamSE algorithm. In conclusion, the
efficiency of the improved Adam algorithm using the standard error has been expressed. Furthermore, the applicability of SGD,
Adam, AdaMax, Nadam, AMSGrad, and AdamSE algorithms in solving the mean-variance portfolio optimization problem
is validated
Accretion and photodesorption of CO ice as a function of the incident angle of deposition
Non-thermal desorption of inter- and circum-stellar ice mantles on dust
grains, in particular ultraviolet photon-induced desorption, has gained
importance in recent years. These processes may account for the observed gas
phase abundances of molecules like CO toward cold interstellar clouds. Ice
mantle growth results from gas molecules impinging on the dust from all
directions and incidence angles. Nevertheless, the effect of the incident angle
for deposition on ice photo-desorption rate has not been studied. This work
explores the impact on the accretion and photodesorption rates of the incidence
angle of CO gas molecules with the cold surface during deposition of a CO ice
layer. Infrared spectroscopy monitored CO ice upon deposition at different
angles, ultraviolet-irradiation, and subsequent warm-up. Vacuum-ultraviolet
spectroscopy and a Ni-mesh measured the emission of the ultraviolet lamp.
Molecules ejected from the ice to the gas during irradiation or warm-up were
characterized by a quadrupole mass spectrometer. The photodesorption rate of CO
ice deposited at 11 K and different incident angles was rather stable between 0
and 45. A maximum in the CO photodesorption rate appeared around
70-incidence deposition angle. The same deposition angle leads to the
maximum surface area of water ice. Although this study of the surface area
could not be performed for CO ice, the similar angle dependence in the
photodesorption and the ice surface area suggests that they are closely
related. Further evidence for a dependence of CO ice morphology on deposition
angle is provided by thermal desorption of CO ice experiments
Micro-PIXE (Particle-Induced X-Ray Emission Analysis) Applications in Minerals Research
The versatility of the PIXE method with microbeams of protons as a non-destructive, in-situ probe for trace element analysis in the geosciences has been demonstrated in an ever increasing number of cases. While in most applications the method can be considered as derivative or as an extension of electron microprobe methodology, features unique to the proton microprobe enable new approaches to hitherto intractable problems of analysis. An appropriate niche has been established in igneous mineralogy and petrology, with important implications both in the basic geosciences as well as mineral industry applications, particularly in the diamond exploration industry. This paper reviews recent advances and discusses the advantages and limitations of current micro-PIXE applications in the geosciences in view of other competing and complimentary methods
Occupational exposure to saw dust: a case study
ABSTRACT: Occupational exposure to saw dust is associated with the development of oncological diseases, namely nasopharyngeal cancers (about 44% are from nasal cavity and paranasal sinus cancers), in the wood and furniture industries, about 55.000, according to the (Associação das Indústrias de Madeira e Mobiliário de Portugal) AIMMP. It should be noted that since 1995 these dusts have been classified as carcinogenic, by The International Agency for Research on Cancer (IARC). The main objective of this study is to evaluate the exposure to saw dust, quantifying its concentration, comparing with values stipulated by existing legislation and standardization. In order to reach the objectives described above, total dust sampling was performed following the NIOSH0500 methodology, in several jobs, in three different carpentries. From the samplings performed, an average value of saw dust concentration was obtained in each workstation. After analyzing the values obtained in the measurements, performed in the real work context, it was verified there was legal non-compliance in the Garlopa workstation and values of the order of magnitude of the NP 1796 exposure limit values ELV, in the Manual Polishing workstation, in some of the Carpentry Workshops. However, if we consider the Scientific Committee on Occupational Exposure Limit (SCOEL) ELV we can state that only the Trimmer complies with the established ELV. Thus, corrective and/or preventive measures should be implemented by employers and preventive measures should be receptive by workers by implementing/complying to ensure the health and well-being of all, will be proposed.info:eu-repo/semantics/publishedVersio
Synthesis and mesomorphic properties of new heterocyclic liquidcrystals with Central Ester–Chalcone linkages
A series of new calamitic liquid crystals, 4-[3-(pyridin-4-yl)prop-2-enoyl]phenyl 4-alkyloxybenzoates, comprising a pyridyl core,ester–chalcone central linkage and terminal alkyloxy chain were synthesized and characterized. This series consists of four membersthat differ by the length of the alkyloxy chain (CnH2n+1O , where n = 10, 12, 14, 16). The structures of the title compounds wereelucidated using spectroscopic and spectrometric techniques, such as FT-IR, NMR (1H and13C) and EI-MS. The mesomorphicproperties were studied using differential scanning calorimetry and optical polarizing microscopy. The decyloxy-containing com-pound was found to be non-mesogenic, whilst the compounds containing n-dodecyloxy to n-hexadecyloxy chains exhibited anenantiotropic smectic A phase with a fan-shaped texture. From the structure–property relationship study, it was proposed that thenumber of carbons in the alkyloxy chain must be at least 12 (n ≥ 12) to generate the smectic phase in the corresponding substitutedArCOOArCOCH CHC5H4N compounds
Synthesis and comparative studies of phase transition behaviour of new dimeric liquid crystals consisting of dimethyluracil and biphenyl cores
A new homologous series of mesogens containing 6-amino-1,3-dimethyluracil moiety have been synthesized. The structures of the compounds were characterised by elemental analysis, FT-IR, 1H and 13C NMR spectroscopic techniques. Their mesomorphic properties were studied by polarising optical microscopy attached to a heating stage. Microscopy data were supported with transition temperatures and enthalpy change values obtained from the differential scanning calorimetry analysis. The studies have shown that the mesomorphic properties of the compounds are dependent on the lengths of alkoxy-spacers. Compounds 4a-f with a shorter alkoxy-spacer chain (n = 6) exhibited smectic A phase, while compounds 4g-r with a alkoxy-spacer chain (n = 8 or 10) displayed nematic phase
Phonoritons as Hybridized Exciton-Photon-Phonon Excitations in a Monolayer h -BN Optical Cavity
A phonoriton is an elementary excitation that is predicted to emerge from hybridization between exciton, phonon, and photon. Besides the intriguing many-particle structure, phonoritons are of interest as they could serve as functional nodes in devices that utilize electronic, phononic, and photonic elements for energy conversion and thermal transport applications. Although phonoritons are predicted to emerge in an excitonic medium under intense electromagnetic wave irradiation, the stringent condition for their existence has eluded direct observation in solids. In particular, on-resonance, intense pumping schemes have been proposed, but excessive photoexcitation of carriers prevents optical detection. Here, we theoretically predict the appearance of phonoritonic features in monolayer hexagonal boron nitride (h-BN) embedded in an optical cavity. The coherent superposition nature of phonoriton states is evidenced by the hybridization of exciton-polariton branches with phonon replicas that is tunable by the cavity-matter coupling strength. This finding simultaneously provides an experimental pathway for observing the predicted phonoritons and opens a new avenue for tuning materials properties
Müllerian Serous Cystadenoma of the Scrotum Following Orchiopexy
A 24-year-old man presented himself with a nodular lesion of about 1 cm diameter at the site of a previous orchiopexy associated with surgery for cryptorchism. Histopathology revealed the lesion to be adenomatous and confined to the scrotum. Histological and immunohistological features were not consistent neither with median raphe cysts or cutaneous adenomas nor with the intrascrotal adenomas of the rete testis, epididymis, nor with (malignant) mesotheliomas. However, the lesion did compare well with serous (papillary) cystadenomas of the testis or paratestis. These adenomas are thought to originate in remnants of the Müllerian system or of peritoneal lining altered by Müllerian metaplasia. This implies that the scrotal adenoma may have developed from an implant of such elements during orchiopexy 14 years ago. Complete excision of the lesion appears to be an adequate therapy
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