534 research outputs found
Measurement of the dynamic charge response of materials using low-energy, momentum-resolved electron energy-loss spectroscopy (M-EELS)
One of the most fundamental properties of an interacting electron system is
its frequency- and wave-vector-dependent density response function, . The imaginary part, , defines the
fundamental bosonic charge excitations of the system, exhibiting peaks wherever
collective modes are present. quantifies the electronic compressibility
of a material, its response to external fields, its ability to screen charge,
and its tendency to form charge density waves. Unfortunately, there has never
been a fully momentum-resolved means to measure at the
meV energy scale relevant to modern elecronic materials. Here, we demonstrate a
way to measure with quantitative momentum resolution by applying
alignment techniques from x-ray and neutron scattering to surface
high-resolution electron energy-loss spectroscopy (HR-EELS). This approach,
which we refer to here as "M-EELS," allows direct measurement of with meV resolution while controlling the momentum with an accuracy
better than a percent of a typical Brillouin zone. We apply this technique to
finite-q excitations in the optimally-doped high temperature superconductor,
BiSrCaCuO (Bi2212), which exhibits several phonons
potentially relevant to dispersion anomalies observed in ARPES and STM
experiments. Our study defines a path to studying the long-sought collective
charge modes in quantum materials at the meV scale and with full momentum
control.Comment: 26 pages, 10 sections, 7 figures, and an appendi
Implementation of a national HIV pre-exposure prophylaxis service is associated with changes in characteristics of people with newly diagnosed HIV: a retrospective cohort study
OBJECTIVES: To review characteristics of individuals newly diagnosed with HIV following implementation of a national pre-exposure prophylaxis (PrEP) programme (comprehensive PrEP services, delivered in sexual health clinics) to inform future delivery and broader HIV prevention strategies. METHODS: We extracted data from national HIV databases (July 2015âJune 2018). We compared sociodemographic characteristics of individuals diagnosed in the period before and after PrEP implementation, and determined the proportion of âpotentially preventableâ infections with the sexual health clinicâbased PrEP delivery model used. RESULTS: Those diagnosed with HIV before PrEP implementation were more likely to be male (342/418, 81.8% vs 142/197, 72.1%, p=0.005), be white indigenous (327/418, 78.2% vs 126/197, 64.0%, p<0.001), report transmission route as sex between men (219/418, 52.4% vs 81/197, 41.1%, p=0.014), and have acquired HIV in the country of the programme (302/418, 72.2% vs 114/197, 57.9% p<0.001) and less likely to report transmission through heterosexual sex (114/418, 27.3% vs 77/197, 39.1%, p=0.002) than after implementation. Pre-implementation, 8.6% (36/418) diagnoses were âpotentially preventableâ with the PrEP model used. Post-implementation, this was 6.6% (13/197), but higher among those with recently acquired HIV (49/170, 28.8%). Overall, individuals with âpotentially preventableâ infections were more likely to be male (49/49, 100% vs 435/566, 76.9%, p<0.001), aged <40 years (37/49, 75.5% vs 307/566, 54.2%, p=0.004), report transmission route as sex between men (49/49, 100% vs 251/566, 44.3%, p<0.001), have previously received post-exposure prophylaxis (12/49, 24.5% vs 7/566, 1.2%, p<0.001) and less likely to be black African (0/49, 0% vs 67/566, 11.8%, p=0.010) than those not meeting this definition. CONCLUSIONS: The sexual health clinicâbased national PrEP delivery model appeared to best suit men who have sex with men and white indigenous individuals but had limited reach into other key vulnerable groups. Enhanced models of delivery and HIV combination prevention are required to widen access to individuals not benefiting from PrEP at present
Promoting Word Consciousness to Close the Vocabulary Gap in Young Word Learners
A proposed avenue for increasing studentsâ vocabulary knowledge and reading comprehension is instruction that promotes studentsâ enthusiasm and attention to words, referred to as word consciousness. This study seeks to investigate, at the utterance level, whether and how word consciousness talk is used in classrooms with young word learners and whether this type of talk is associated with student gains in general vocabulary knowledge. Using videotaped classroom (N = 27) observations, this study found evidence of word consciousness talk, with variability of use across classrooms. Multilevel modeling revealed that this kind of teacher talkâoperationalized as reinforcing studentsâ use of words, affirming studentsâ recognition of word meanings, and helping students make personal connections to wordsâwas positively associated with student gains in general vocabulary knowledge at the end of kindergarten. Findings from this study can provide guidance for teachers seeking strategies to increase studentsâ general vocabulary knowledge, beyond words taught
New cationic polyprenyl derivative proposed as a lipofecting agent
Cationic linear poly-cis-isoprenoid prepared from natural plant polyprenol in a mixture with dioleyl phosphatidylethanolamine was found to be an effective lipofection agent for eukaryotic cells. The transfecting activity is related to the poly-cis structure of the polyprenyl chain
HCMV pUL135 remodels the actin cytoskeleton to impair immune recognition of infected cells
Immune evasion genes help human cytomegalovirus (HCMV) establish lifelong persistence. Without immune pressure, laboratory-adapted HCMV strains have undergone genetic alterations. Among these, the deletion of the UL/bâ domain is associated with loss of virulence. In a screen of UL/bâ, we identified pUL135 as a protein responsible for the characteristic cytopathic effect of clinical HCMV strains that also protected from natural killer (NK) and TÂ cell attack. pUL135 interacted directly with abl interactor 1 (ABI1) and ABI2 to recruit the WAVE2 regulatory complex to the plasma membrane, remodel the actin cytoskeleton and dramatically reduce the efficiency of immune synapse (IS) formation. An intimate association between F-actin filaments in target cells and the IS was dispelled by pUL135 expression. Thus, F-actin in target cells plays a critical role in synaptogenesis, and this can be exploited by pathogens to protect against cytotoxic immune effector cells. An independent interaction between pUL135 and talin disrupted cell contacts with the extracellular matrix
Actin depletion initiates events leading to granule secretion at the immunological synapse.
Cytotoxic T lymphocytes (CTLs) use polarized secretion to rapidly destroy virally infected and tumor cells. To understand the temporal relationships between key events leading to secretion, we used high-resolution 4D imaging. CTLs approached targets with actin-rich projections at the leading edge, creating an initially actin-enriched contact with rearward-flowing actin. Within 1 min, cortical actin reduced across the synapse, T cell receptors (TCRs) clustered centrally to form the central supramolecular activation cluster (cSMAC), and centrosome polarization began. Granules clustered around the moving centrosome within 2.5 min and reached the synapse after 6 min. TCR-bearing intracellular vesicles were delivered to the cSMAC as the centrosome docked. We found that the centrosome and granules were delivered to an area of membrane with reduced cortical actin density and phospholipid PIP2. These data resolve the temporal order of events during synapse maturation in 4D and reveal a critical role for actin depletion in regulating secretion.Funding was provided by the Wellcome Trust through Principal Research Fellowships
(075880 and 103930) to G.M.G. and a Strategic Award (100140) to
the Cambridge Institute for Medical Research (CIMR). A.T.R. is an NIH-OxCam
scholar supported by funding to J.L.-S. from the Eunice Shriver National Institute
of Child Health and Human Development.This is the final version. It was first published by Elsevier at http://www.cell.com/immunity/abstract/S1074-7613%2815%2900173-9
- âŚ