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1.
Environ Geochem Health ; 45(4): 1165-1171, 2023 Apr.
Artigo em Inglês | MEDLINE | ID: mdl-35044549

RESUMO

When the SEGH international board released a short editorial paper back in 2019, we described an aim to increase the membership offering, whilst improving the diversity of input regionally, by scientific discipline and to ensure greater and more regular contact across the regions from 2020 onwards. Wider aspirations described in 2019 (Watts et al. 2019) are discussed within this short communication at the end of 2021 to evaluate progress made. In particular, how the SEGH community adapted to the unprecedented circumstances that have challenged each and every one of us throughout the COVID-19 pandemic since early 2020 and are likely to influence our activities for the foreseeable future.


Assuntos
Saúde Ambiental , Ciência Ambiental , Sociedades , Humanos , COVID-19/epidemiologia , Pandemias
2.
J Geophys Res Planets ; 127(6): e2022JE007189, 2022 Jun.
Artigo em Inglês | MEDLINE | ID: mdl-35865671

RESUMO

We present a reanalysis (using the Minnaert limb-darkening approximation) of visible/near-infrared (0.3-2.5 µm) observations of Uranus and Neptune made by several instruments. We find a common model of the vertical aerosol distribution i.e., consistent with the observed reflectivity spectra of both planets, consisting of: (a) a deep aerosol layer with a base pressure >5-7 bar, assumed to be composed of a mixture of H2S ice and photochemical haze; (b) a layer of photochemical haze/ice, coincident with a layer of high static stability at the methane condensation level at 1-2 bar; and (c) an extended layer of photochemical haze, likely mostly of the same composition as the 1-2-bar layer, extending from this level up through to the stratosphere, where the photochemical haze particles are thought to be produced. For Neptune, we find that we also need to add a thin layer of micron-sized methane ice particles at ∼0.2 bar to explain the enhanced reflection at longer methane-absorbing wavelengths. We suggest that methane condensing onto the haze particles at the base of the 1-2-bar aerosol layer forms ice/haze particles that grow very quickly to large size and immediately "snow out" (as predicted by Carlson et al. (1988), https://doi.org/10.1175/1520-0469(1988)045<2066:CMOTGP>2.0.CO;2), re-evaporating at deeper levels to release their core haze particles to act as condensation nuclei for H2S ice formation. In addition, we find that the spectral characteristics of "dark spots", such as the Voyager-2/ISS Great Dark Spot and the HST/WFC3 NDS-2018, are well modelled by a darkening or possibly clearing of the deep aerosol layer only.

3.
Science ; 374(6570): 968-972, 2021 Nov 19.
Artigo em Inglês | MEDLINE | ID: mdl-34709937

RESUMO

Jupiter's atmosphere has a system of zones and belts punctuated by small and large vortices, the largest being the Great Red Spot. How these features change with depth is unknown, with theories of their structure ranging from shallow meteorological features to surface expressions of deep-seated convection. We present observations of atmospheric vortices using the Juno spacecraft's Microwave Radiometer. We found vortex roots that extend deeper than the altitude at which water is expected to condense, and we identified density inversion layers. Our results constrain the three-dimensional structure of Jupiter's vortices and their extension below the clouds.

5.
J Immigr Minor Health ; 22(3): 571-579, 2020 Jun.
Artigo em Inglês | MEDLINE | ID: mdl-31183593

RESUMO

Research has found that 24% of foreign domestic workers (FDWs) in Singapore have poor mental health (24%), with depressive symptoms being identified as the second most severe psychological symptoms [1]. The study assessed the acceptability and effectiveness of a 4-week cognitive behavioral therapy (CBT)-based paraprofessional training program for FDWs in Singapore on depression literacy and CBT knowledge (primary outcomes), depression-related stigma, as well as attitudes towards seeking professional help (secondary outcomes) immediately and 2 months following the training. Forty female Filipino FDWs were recruited and randomized into either a CBT-based paraprofessional training program or wait-list (WL) group. Participants completed outcome measures before, after, and 2 months following their training. No significant difference was found on changes on any of the outcome variables in the intervention group as compared to the WL group. Following training, both groups showed significantly improved depression literacy, CBT knowledge, and attitudes towards seeking professional help. These changes were sustained at 2-month follow-up. All participants indicated a high level of satisfaction with the training program. While findings from between-group analyses do not support the efficacy of the CBT-based paraprofessional training program in improving depression literacy and related outcomes, participation in the program was associated with improvements in several outcomes within the training group. Future research should explore adaptations to the program (e.g., in terms of training duration and modes of delivery) that would increase its efficacy in improving depression literacy and CBT knowledge among FDWs.


Assuntos
Terapia Cognitivo-Comportamental/educação , Zeladoria , Saúde Mental/etnologia , Grupo Associado , Adulto , Depressão/terapia , Emigrantes e Imigrantes , Feminino , Humanos , Pessoa de Meia-Idade , Filipinas/etnologia , Avaliação de Programas e Projetos de Saúde , Singapura
6.
Sci Total Environ ; 707: 134954, 2020 Mar 10.
Artigo em Inglês | MEDLINE | ID: mdl-31869610

RESUMO

Protein rich food waste could be used as raw materials for making fish feed pellets, which would diminish the volume of dumped waste into landfills. This study investigated the use of food waste (FW) based pellets composing of 75% food wastes derived from plant materials (cereals, fruit and vegetables) supplemented with yeast and the mixture of bromelain and papain to feed grass carp (Ctenopharyngodon idellus). Generally, improved growth performance (in terms of feed conversion ratio, protein efficiency ratio and relative weight gain) was observed in the diet groups supplemented with yeast (Saccharomyces cerevisiae). The most optimal dose was 25 g/kg yeast with enzymes (bromelain and papain, at the ratio of 1:1) and protein utilization was enhanced. Fish immunity was also stimulated, which indicated by the higher nitroblue tetrazolium and bactericidal activities. Moreover, resistance against Aeromonas hydrophilia was enhanced. It is envisaged that food waste could be widely used as feeds for culturing herbivorous fish and adding supplements such as baker's yeast and enzymes will further enhance the feed conversion ratio and fish immunity.


Assuntos
Carpas , Doenças dos Peixes , Eliminação de Resíduos , Ração Animal , Animais , Dieta , Suplementos Nutricionais , Imunidade Inata , Saccharomyces cerevisiae
7.
Astron J ; 156(2)2018 Aug.
Artigo em Inglês | MEDLINE | ID: mdl-30510303

RESUMO

We characterize the origin and evolution of a mesoscale wave pattern in Jupiter's North Equatorial Belt (NEB), detected for the first time at 5 µm using a 2016-17 campaign of "lucky imaging" from the VISIR instrument on the Very Large Telescope and the NIRI instrument on the Gemini observatory, coupled with M-band imaging from Juno's JIRAM instrument during the first seven Juno orbits. The wave is compact, with a 1°.1-1°.4 longitude wavelength (wavelength 1300-1600 km, wavenumber 260-330) that is stable over time, with wave crests aligned largely north-south between 14°N and 17°N (planetographic). The waves were initially identified in small (10° longitude) packets immediately west of cyclones in the NEB at 16°N but extended to span wider longitude ranges over time. The waves exhibit a 7-10 K brightness temperature amplitude on top of an ∼210 K background at 5 µm. The thermal structure of the NEB allows for both inertio-gravity waves and gravity waves. Despite detection at 5 µm, this does not necessarily imply a deep location for the waves, and an upper tropospheric aerosol layer near 400-800 mbar could feature a gravity wave pattern modulating the visible-light reflectivity and attenuating the 5-µm radiance originating from deeper levels. Strong rifting activity appears to obliterate the pattern, which can change on timescales of weeks. The NEB underwent a new expansion and contraction episode in 2016-17 with associated cyclone-anticyclone formation, which could explain why the mesoscale wave pattern was more vivid in 2017 than ever before.

8.
Environ Pollut ; 231(Pt 1): 732-741, 2017 Dec.
Artigo em Inglês | MEDLINE | ID: mdl-28858668

RESUMO

This study aims to assess the role of Fe plaque in metal uptake and translocation by different wetland plants and examine the effects of organic acids on metal detoxification in wetland plants. It was found that although exposed to a similar level of metals in rhizosphere soil solution, metal uptake by shoots of Cypercus flabelliformis and Panicum paludosum was greatly reduced, consequently leading to a better growth under flooded than under drained conditions. This may be related to the enhanced Fe plaque in the former, but due to the decreased root permeability in the latter under anoxic conditions. The Fe plaque on root surface has potential to sequester metals and then reduce metal concentrations and translocation in shoot tissues. However, whether the Fe plaque acts as a barrier to metal uptake and translocation may also be dependent on the root anatomy. Although metal tolerance in wetland plants mainly depends upon their metal exclusion ability, the higher-than-toxic-level of metal concentrations in some species indicates that internal metal detoxification might also exist. It was suggested that malic or citric acid in shoots of P. paludosum and C. flabelliformis may account for their internal detoxification for Zn.


Assuntos
Metais/metabolismo , Plantas/metabolismo , Poluentes do Solo/metabolismo , Áreas Alagadas , Ácidos Acíclicos , Ferro , Compostos Orgânicos , Raízes de Plantas/química , Rizosfera , Solo , Poluentes do Solo/análise
9.
Environ Sci Pollut Res Int ; 24(10): 8990-9001, 2017 Apr.
Artigo em Inglês | MEDLINE | ID: mdl-26520098

RESUMO

Angiogenesis, formation of new blood vessels from preexisting one, is a critical step of tumorgenesis of solid tumors. Therefore, antiangiogenic therapy is one of the promising approaches to control tumor growth. In the past 20 years, a lot of compounds have been tested for their antiangiogenic properties. Bevacizumab, Avastin®, the first antiangiogenic drug approved by the US FDA, has been widely used in clinic for treating cancer. Indeed, many synthetic compounds are highly toxic and exert side effects even though they are effective in inhibiting neovessel formation and cancer cell growth. Using natural compounds or their derivatives is one of the ways to solve these problems. Sinomenine and ginsenosides are common antiangiogenic and anticancer compounds that are extracted from herbal medicines. Recent findings suggested that marine algae-derived natural pigments also possess similar activities. It has been reported that fucoxanthin from Undaria pinnatifida, Siphonaxanthin from Codium fragile, can inhibit angiogenesis and cancer growth effectively. In conclusion, natural compounds derived from marine algae could provide a novel and safe source for new drug development in anticancer and antiangiogenic properties in the future.


Assuntos
Inibidores da Angiogênese , Neovascularização Patológica , Humanos , Neoplasias
10.
Nat Commun ; 7: 13262, 2016 11 08.
Artigo em Inglês | MEDLINE | ID: mdl-27824031

RESUMO

Saturn has an intense and broad eastward equatorial jet with a complex three-dimensional structure mixed with time variability. The equatorial region experiences strong seasonal insolation variations enhanced by ring shadowing, and three of the six known giant planetary-scale storms have developed in it. These factors make Saturn's equator a natural laboratory to test models of jets in giant planets. Here we report on a bright equatorial atmospheric feature imaged in 2015 that moved steadily at a high speed of 450 ms-1 not measured since 1980-1981 with other equatorial clouds moving within an ample range of velocities. Radiative transfer models show that these motions occur at three altitude levels within the upper haze and clouds. We find that the peak of the jet (latitudes 10° N to 10° S) suffers intense vertical shears reaching +2.5 ms-1 km-1, two orders of magnitude higher than meridional shears, and temporal variability above 1 bar altitude level.

11.
Environ Pollut ; 219: 829-836, 2016 Dec.
Artigo em Inglês | MEDLINE | ID: mdl-27707601

RESUMO

In the present study, the Hg contamination in mariculture sites located at the estuary of Pearl River was to investigate with an attempt to analyse associated health risks of dietary exposure to both total mercury (THg) and methyl mercury (MeHg) in cultured fish and shellfish. The highest total mercury concentration (7.037 ± 0.556 ng L-1) of seawater was observed at Zhuhai Estuary. The Hg concentrations of sediment in Guishan Island were significantly higher (p < 0.05) than in Daya Bay (away from the Pearl River). Besides, the both THg and MeHg levels in sediment at mariculture sites were higher (p < 0.05) than corresponding reference sites. It was attributed to the fact that mariculture activities increased Hg loading and promoted MeHg production. The vertical distribution of Hg in sediment cores demonstrated that mercury methylation mostly occurred at the sediment-water interface. Results of health risk assessments showed that fish consumption would impose a higher risk to children but less to adults, while shellfish produced in the studied area was safe for consumption.


Assuntos
Estuários , Pesqueiros , Peixes/metabolismo , Mercúrio/análise , Rios , Água do Mar/química , Poluentes Químicos da Água/análise , Animais , China , Monitoramento Ambiental , Compostos de Metilmercúrio/análise , Medição de Risco , Frutos do Mar/análise
12.
Nano Lett ; 16(10): 6331-6336, 2016 10 12.
Artigo em Inglês | MEDLINE | ID: mdl-27648493

RESUMO

Charge density wave (CDW) formation in solids is a critical phenomenon involving the collective reorganization of the electrons and atoms in the system into a wave structure, and it is expected to be sensitive to the geometric constraint of the system at the nanoscale. Here, we study the CDW transition in TiSe2, a quasi-two-dimensional layered material, to determine the effects of quantum confinement and changing dimensions in films ranging from a single layer to multilayers. Of key interest is the characteristic length scale for the transformation from a two-dimensional case to the three-dimensional limit. Angle-resolved photoemission spectroscopy (ARPES) measurements of films with thicknesses up to six layers reveal substantial variations in the energy structure of discrete quantum well states; however, the temperature-dependent band gap renormalization converges at just three layers. The results indicate a layer-dependent mixture of two transition temperatures and a very-short-range CDW interaction within a three-dimensional framework.

13.
Environ Pollut ; 219: 815-820, 2016 Dec.
Artigo em Inglês | MEDLINE | ID: mdl-27498342

RESUMO

The main aim of this study was to investigate the feasibility of using soybean meal added with papain to replace half of the fishmeal used in the moist pellets (49% fishmeal and 45% trash fish) developed by the Hong Kong Agriculture, Fisheries and Conservation Department (AFCD) for culturing marine fish. Gold-lined seabream (Rhabdosargus sarba), brown spotted grouper (Epinephelus bleekeri) and pompano (Trachinotus blochii) were farmed at one of the research stations (Kat-O) of AFCD, for a period of 340 days. Results indicated that diets containing papain resulted in better fish growth (reflected by relative weight gain and feed conversion ratio) than diets without papain. In general, wet weight gain of fish depends on the amount of papain added in diet rather than the diet composition. Soybean used in conjunction with papain also contributed to a more effective growth than fish fed with the moist pellets alone. A laboratory experiment (using tanks) was conducted to study the effects of the diets on concentrations of ammonia, nitrite and nitrate in the tank water. Results showed that concentrations of ammonia and nitrate were significantly lower (p < 0.05) when the fish were fed with papain-supplemented (with or without soybean meal) diets. It is envisaged that by using plant protein incorporated with enzymes could promote better growth of marine fish and lower the adverse impact of trash fish and fishmeal on water quality of the mariculture zones.


Assuntos
Ração Animal/análise , Aquicultura/métodos , Glycine max/metabolismo , Papaína/metabolismo , Perciformes/crescimento & desenvolvimento , Perciformes/metabolismo , Qualidade da Água , Animais , Hong Kong
14.
Environ Sci Pollut Res Int ; 23(8): 7178-85, 2016 Apr.
Artigo em Inglês | MEDLINE | ID: mdl-26432269

RESUMO

Different types of food wastes, e.g., meats, bones, cereals, fruits, and vegetables, were collected from hotels in Hong Kong, mixed in different ratio, and processed into feed pellets (food wastes (FWs) A, B, and C) for feeding trials in aquaculture species. Grass carp fed with cereal-dominant feed (FW A) showed the best growth (in terms of specific growth rate, relative weight gain, and protein efficiency ratio), among all food waste feeds. However, the growth rates of food waste groups especially the meat product-contained feeds (FW B and FW C) were lower than the commercial feed, Jinfeng(®) 613 formulation (control). The results indicated that grass carp utilized plant proteins better than animal proteins and preferred carbohydrate as a major energy source than lipid. The high-lipid content in feed containing meat products was also a possible reason for hindering growth and resulted high body lipid. It is suggested that lipid should be removed in the preparation of food waste feed or further investigations by implementing supplements, e.g., enzymes in feed to enhance lipid or protein utilization by fish. This utilization of food waste could be an effective and practical way to deal with these wastes in this densely populated city.


Assuntos
Ração Animal/análise , Carpas/crescimento & desenvolvimento , Pesqueiros , Tecnologia de Alimentos/métodos , Reciclagem/métodos , Resíduos Sólidos/análise , Animais , Carpas/metabolismo , Carboidratos da Dieta/análise , Carboidratos da Dieta/metabolismo , Proteínas Alimentares/análise , Proteínas Alimentares/metabolismo , Inocuidade dos Alimentos , Hong Kong , Humanos , Proteínas de Plantas/análise , Proteínas de Plantas/metabolismo
15.
Chemosphere ; 145: 224-30, 2016 Feb.
Artigo em Inglês | MEDLINE | ID: mdl-26688259

RESUMO

Arbuscular mycorrhizal fungi (AMF) - Rhizophagus intraradices was inoculated to rice to investigate its effects on arsenic (As) uptake, grain As speciation, and rhizospheric As concentration of six rice cultivars grown in As-amended soil (60 mg As kg(-1) soil). The AMF inoculation induced either positive, neutral or negative responses in rice grown in As contaminated soil, suggesting that functional diversity may exist in AMF symbiosis when As is taken up and transferred. The ratios of inorganic/organic As concentrations in rice grains of all cultivars were significantly reduced by AMF, that involved the transformation of inorganic As into less toxic organic form dimethylarsinic acid (DMA) in rice. AMF decreased significantly total As and inorganic As concentrations in rice grains of Handao 3. Positive correlations (R(2) = 0.30-0.56, P < 0.05) between As in the rhizospheric soil solution and As in rice grain at different periods were observed. This inferred that the As survey of soil solution can be an effective measure for evaluating As in grains.


Assuntos
Arsênio/farmacocinética , Grão Comestível/metabolismo , Glomeromycota/fisiologia , Micorrizas/fisiologia , Oryza/metabolismo , Poluentes do Solo/farmacocinética , Arsênio/análise , Ácido Cacodílico/metabolismo , Grão Comestível/microbiologia , Oryza/microbiologia , Rizosfera , Microbiologia do Solo , Poluentes do Solo/análise
16.
Hong Kong Med J ; 22(2): 106-15, 2016 Apr.
Artigo em Inglês | MEDLINE | ID: mdl-26635306

RESUMO

OBJECTIVE: To investigate the impact of skeletal-related events on survival in patients with metastatic prostate cancer prescribed long-term androgen deprivation therapy. METHODS: This historical cohort study was conducted in two hospitals in Hong Kong. Patients who were diagnosed with metastatic prostate cancer and prescribed androgen deprivation therapy between January 2006 and December 2011 were included. Details of skeletal-related events and mortality were examined. RESULTS: The median follow-up was 28 (range, 1-97) months. Of 119 patients, 52 (43.7%) developed skeletal-related events throughout the study, and the majority received bone irradiation for pain control. The median actuarial overall survival and cancer-specific survival for patients with skeletal-related events were significantly shorter than those without skeletal-related events (23 vs 48 months, P=0.003 and 26 vs 97 months, P<0.001, respectively). Multivariate analysis revealed that the adjusted hazard ratio of presence of skeletal-related events on overall and cancer-specific survival was 2.73 (95% confidence interval, 1.46-5.10; P=0.002) and 3.92 (95% confidence interval, 1.87-8.23; P<0.001), respectively. A prostate-specific antigen nadir of >4 ng/mL was an independent poor prognostic factor for overall and cancer-specific survival after development of skeletal-related events (hazard ratio=10.42; 95% confidence interval, 2.10-51.66 and hazard ratio=10.54; 95% confidence interval, 1.94-57.28, respectively). CONCLUSIONS: Skeletal-related events were common in men with metastatic prostate cancer. This is the first reported study to show that a skeletal-related event is an independent prognostic factor in overall and cancer-specific survival in patients with metastatic prostate cancer prescribed androgen deprivation therapy. A prostate-specific antigen nadir of >4 ng/mL is an independent poor prognostic factor for overall and cancer-specific survival following development of skeletal-related events.


Assuntos
Antagonistas de Androgênios/uso terapêutico , Neoplasias Ósseas/epidemiologia , Dor/etiologia , Neoplasias da Próstata/tratamento farmacológico , Idoso , Idoso de 80 Anos ou mais , Neoplasias Ósseas/patologia , Neoplasias Ósseas/secundário , Estudos de Coortes , Seguimentos , Hong Kong , Humanos , Masculino , Pessoa de Meia-Idade , Análise Multivariada , Prognóstico , Modelos de Riscos Proporcionais , Antígeno Prostático Específico/sangue , Neoplasias da Próstata/patologia , Estudos Retrospectivos , Taxa de Sobrevida
17.
Environ Sci Pollut Res Int ; 23(8): 7186-94, 2016 Apr.
Artigo em Inglês | MEDLINE | ID: mdl-26092357

RESUMO

The fast growing of global aquaculture industry accompanied with increasing pressure on the supply and price of traditional feed materials (e.g., fish meal and soy bean meal). This circumstance has urged the need to search alternative sources of feed stuff. Food waste was used as feed stuff in rearing fish which possess substantial protein and lipid. Grass carp are major species reared in Hong Kong with lower nutritional requirements; it is also an ideal species for investigating the feasibility of using food waste as fish feeds for local aquaculture industry. The growth and immunity, reflected by total protein, total immunologlobulin (IgI), and nitroblue tetrazolium (NBT) activity of grass carp blood, were depressed when feeding with food waste feeds without enzymes. However, the supplementation of bromelain and papain in fish feed enhanced the efficient use of food waste by grass carp, which in turn improved the fish immunity. The present results indicated that the addition of those enzymes could enhance the feed utilization by fish and hematological parameters of grass carp, and the improvement on growth and immunity superior to the control (commercial feed) was observed with the addition of bromelain and papain supplement. Addition of 1 and 2 % mixture of bromelain and papain could significantly enhance the lipid utilization in grass carp.


Assuntos
Ração Animal/análise , Bromelaínas/análise , Carpas , Pesqueiros , Papaína/análise , Resíduos Sólidos/análise , Ração Animal/normas , Animais , Bromelaínas/farmacologia , Carpas/crescimento & desenvolvimento , Carpas/imunologia , Proteínas Alimentares/análise , Proteínas Alimentares/metabolismo , Suplementos Nutricionais/análise , Hong Kong , Metabolismo dos Lipídeos/efeitos dos fármacos , Papaína/farmacologia
18.
Int J Phytoremediation ; 17(11): 1073-80, 2015.
Artigo em Inglês | MEDLINE | ID: mdl-25901895

RESUMO

Arbuscular mycorrhizal fungi (AMF) appear to be highly associated with arsenic (As) uptake in host plants because arsenate (As(V)) and phosphorus (P) share the same transporter, whereby AMF can enhance P uptake. A short-term experiment was conducted for low- (0 to 0.05 mM As) and high-affinity (0 to 2.5 mM As) uptake systems, to investigate the AMF role on As uptake mechanism in plants, which may explain As uptake kinetics in upland rice cultivar: Zhonghan 221. When concentration of As ranged from 0 to 0.05 mM, Funneliformis geosporum (Fg) significantly decreased arsenite (As(III)) and monomethylarsonicacid (MMA) uptake when (p < 0.05) compared to non-mycorrhizal (NM) treatment, since the major route for (As(III)) in rice roots-rice silicon transporter Lsi1 would be influenced by Fg inoculation at high As concentrations. Fg can also reduce As(V) uptake significantly (p < 0.05) under both uptake systems relative to NM treatment, whereas, Funneliformis mosseae (Fm) increased As(V) and MMA uptake in rice roots, with MMA uptake rate generally lower than As(III) and As(V). Using suitable AMF species inoculation with rice, As uptake and accumulation in rice grains can be reduced and the risk to human health, once consumed, can be minimized.


Assuntos
Arsênio/metabolismo , Arsenicais/metabolismo , Glomeromycota/metabolismo , Micorrizas/metabolismo , Oryza/metabolismo , Microbiologia do Solo , Poluentes do Solo/metabolismo , Biodegradação Ambiental , Cinética , Oryza/microbiologia , Especificidade da Espécie
20.
Phys Rev Lett ; 115(25): 257402, 2015 Dec 18.
Artigo em Inglês | MEDLINE | ID: mdl-26722943

RESUMO

We used low-energy, momentum-resolved inelastic electron scattering to study surface collective modes of the three-dimensional topological insulators Bi_{2}Se_{3} and Bi_{0.5}Sb_{1.5}Te_{3-x}Se_{x}. Our goal was to identify the "spin plasmon" predicted by Raghu and co-workers [Phys. Rev. Lett. 104, 116401 (2010)]. Instead, we found that the primary collective mode is a surface plasmon arising from the bulk, free carriers in these materials. This excitation dominates the spectral weight in the bosonic function of the surface χ^{"}(q,ω) at THz energy scales, and is the most likely origin of a quasiparticle dispersion kink observed in previous photoemission experiments. Our study suggests that the spin plasmon may mix with this other surface mode, calling for a more nuanced understanding of optical experiments in which the spin plasmon is reported to play a role.

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