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"Chevalier, A"
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Channels of Impact: User Reviews When Quality Is Dynamic and Managers Respond
We examine the effect of managerial response on consumer voice in a dynamic quality environment. We argue that the consumer is motivated to write reviews not only because reviews may impact other consumers, but because reviews may impact the management and the quality of the service. We examine this empirically in a scenario in which reviewers receive a credible signal that the service provider is listening. Specifically, we examine the “managerial response” feature allowed by many review platforms. We hypothesize that managerial responses will stimulate reviewing activity and, in particular, will stimulate negative reviews that are seen as more impactful. This effect is further heightened because managers respond more and in more detail to negative reviews. Using a multiple-differences specification, we show that reviewing activity and particularly negative reviewing is indeed stimulated by managerial response. Our specification exploits comparison of the same hotel immediately before and after response initiation and compares a given hotel’s reviewing activity on sites with review response initiation to that on sites that do not allow managerial response. We also explore the mechanism behind the effect using an online experiment.
Data and the online appendix are available at
https://doi.org/10.1287/mksc.2018.1090
.
Journal Article
Dielectric characterization and modelling of aqueous solutions involving sodium chloride and sucrose and application to the design of a bi-parameter RF-sensor
This paper reports on dielectric properties of ternary mixtures involving sodium chloride (NaCl) and sucrose (C
12
H
22
O
11
) dissolved into water (H
2
O). Broadband electromagnetic characterizations of such mixtures at various concentrations were performed, evidencing a dual behavior made of conductive effects at low frequencies and dipolar relaxation at microwave frequencies. Conductive and dielectric properties resulting from these both effects were integrated into predictive models for variations of Cole–Cole model parameters. Based upon this modelling, an innovative microwave-based sensor able to retrieve concentrations of both sodium chloride and sucrose in ternary aqueous solutions was introduced, designed, realized and assessed. The proposed sensor shows an error lower than 5.5% for concentration ranges of 0 to 154 mmol/L for sodium chloride and 0 to 877 mmol/L for sucrose.
Journal Article
Chandra’s Insights into SN 2023ixf
We report Chandra-ACIS observations of supernova (SN) 2023ixf in M101 on day 13 and 86 since the explosion. The X-rays in both epochs are characterized by high-temperature plasma from the forward shocked region as a result of circumstellar interaction. We are able to constrain the absorption column density at both Chandra epochs, which is much larger than that due to the Galactic and host absorption column, and we attribute it to absorption by the circumstellar matter in the immediate vicinity of SN 2023ixf. Combining our column density measurements with the published measurement on day 4, we show that the column density declines as t −2 between day 4 to day 13 and then evolves as t −1. The unabsorbed 0.3–10 keV luminosity evolves as t −1 during the Chandra epochs. On the Chandra first epoch observation, when the SN was 13 days old, we detect the Fe Kα fluorescent line at 6.4 keV indicating presence of cold material in the vicinity of the supernova. The line is absent on day 86, consistent with the decreased column density by a factor of 7 between the two epochs. Our analysis indicates that during 10–1.5 yr before explosion, the progenitor was evolving with a constant mass-loss rate of 5.6 × 10−4 M ⊙ yr−1.
Journal Article
The relation between meniscal dynamics and tibiofemoral kinematics
Over the past 30 years, research on meniscal kinematics has been limited by challenges such as low-resolution imaging and capturing continuous motion from static data. This study aimed to develop a computational knee model that overcomes these limitations and enables the continuous assessment of meniscal dynamics. A high-resolution MRI dataset (n = 11) was acquired in 4 configurations of knee flexion. In each configuration, the menisci were modeled based on the underlying osseous anatomy. Principal Polynomial Shape Analysis (PPSA) was employed for continuous meniscal modeling. Maximal medial anterior horn displacement occurred in 60° of flexion, equaling 6.24 mm posteromedial, while the posterior horn remained relatively stable. At 90° of flexion, the lateral anterior and posterior horn displaced posteromedially, amounting 5.70 mm and 6.51 mm respectively. The maximal observed Average Surface Distance (ASD) equaled 0.70 mm for lateral meniscal modeling in 90° of flexion. Based on our results, a strong relation between meniscal dynamics and tibiofemoral kinematics was confirmed. Expanding on static meniscal modeling and employing PPSA, we derived and validated a standardized and systematic methodological workflow.
Journal Article
Sex-Related Abnormalities in Substantia Nigra Lipids in Parkinson’s Disease
Parkinson’s disease (PD) is a neurodegenerative movement disorder involving the selective loss of dopamine-producing neurons in the substantia nigra (SN). Differences in disease presentation, prevalence, and age of onset have been reported between males and females with PD. The content and composition of the major glycosphingolipids, phospholipids, and cholesterol were evaluated in the SN from 12 PD subjects and in 18 age-matched, neurologically normal controls. Total SN ganglioside sialic acid content and water content (%) were significantly lower in the male PD subjects than in the male controls. The content of all major gangliosides were reduced in the male PD subjects to some degree, but the neuronal-enriched gangliosides, GD1a and GT1b, were most significantly reduced. The distribution of phosphatidylethanolamine, phosphatidylcholine, and phosphatidylinositol was also significantly lower in the male PD subjects than in the male controls. However, the distribution of myelin-enriched cerebrosides and sulfatides was significantly higher in the male PD subjects than in the male controls suggesting myelin sparing in the male PD subjects. No elevation was detected for astrocytosis-linked GD3. These neurochemical changes provide evidence of selective neuronal loss in SN of the males with PD without robust astrocytosis. In contrast to the SN lipid abnormalities found in the male PD subjects, no significant abnormalities were found in the female PD subjects for SN water content or for any major SN lipids. These data indicate sex-related differences in SN lipid abnormalities in PD.
Journal Article
Gem-Induced Cytoskeleton Remodeling Increases Cellular Migration of HTLV-1-Infected Cells, Formation of Infected-to-Target T-Cell Conjugates and Viral Transmission
Efficient HTLV-1 viral transmission occurs through cell-to-cell contacts. The Tax viral transcriptional activator protein facilitates this process. Using a comparative transcriptomic analysis, we recently identified a series of genes up-regulated in HTLV-1 Tax expressing T-lymphocytes. We focused our attention towards genes that are important for cytoskeleton dynamic and thus may possibly modulate cell-to-cell contacts. We first demonstrate that Gem, a member of the small GTP-binding proteins within the Ras superfamily, is expressed both at the RNA and protein levels in Tax-expressing cells and in HTLV-1-infected cell lines. Using a series of ChIP assays, we show that Tax recruits CREB and CREB Binding Protein (CBP) onto a c-AMP Responsive Element (CRE) present in the gem promoter. This CRE sequence is required to drive Tax-activated gem transcription. Since Gem is involved in cytoskeleton remodeling, we investigated its role in infected cells motility. We show that Gem co-localizes with F-actin and is involved both in T-cell spontaneous cell migration as well as chemotaxis in the presence of SDF-1/CXCL12. Importantly, gem knock-down in HTLV-1-infected cells decreases cell migration and conjugate formation. Finally, we demonstrate that Gem plays an important role in cell-to-cell viral transmission.
Journal Article
Relativistic ejecta from X-ray flash XRF 060218 and the rate of cosmic explosions
X-Rated Supernova
A link between long γ-ray bursts (GRBs) and supernovae has been established, but whether there is a similar relationship between the weaker and softer X-ray flashes and supernovae is unclear. GRB/XRF 060218, spotted by the Swift satellite on 18 February this year, may supply that missing link. In the first of four papers on this novel burster, Campana
et al
. report the sighting of the X-ray signature of a shock break-out, possible evidence of a supernova in progress. Pian
et al
. report the optical discovery of a type Ic supernova 2006aj associated with GRB/XRF 060218. Soderberg
et al
. report radio and X-ray observations that show that XRF 060218 is 100 times less energetic than, but of a type that is ten times more common than cosmological GRBs. Mazzali
et al
. modelled the spectra and light curve of SN 2006aj to show that it had a much smaller explosion energy and ejected much less mass than other GRB-supernovae, suggesting that it was produced by a star with a mass was only about 20 times that of the Sun, leaving behind a neutron star, rather than a black hole.
Radio and X-ray observations of X-ray flash XRF 060218, which is associated with supernova SN 2006aj, show that this event is 100 times less energetic but ten times more common than cosmological gamma-ray bursts (GRBs). The production of relativistic ejecta seems to be the key physical distinction between GRBs/XRFs and ordinary supernovae.
Over the past decade, long-duration γ-ray bursts (GRBs)—including the subclass of X-ray flashes (XRFs)—have been revealed
1
,
2
,
3
to be a rare variety of type Ibc supernova. Although all these events result from the death of massive stars, the electromagnetic luminosities of GRBs and XRFs exceed those of ordinary type Ibc supernovae by many orders of magnitude. The essential physical process that causes a dying star to produce a GRB or XRF, and not just a supernova, is still unknown. Here we report radio and X-ray observations of XRF 060218 (associated
4
with supernova SN 2006aj), the second-nearest
5
,
6
GRB identified until now. We show that this event is a hundred times less energetic but ten times more common than cosmological GRBs. Moreover, it is distinguished from ordinary type Ibc supernovae by the presence of 10
48
erg coupled to mildly relativistic ejecta, along with a central engine (an accretion-fed, rapidly rotating compact source) that produces X-rays for weeks after the explosion. This suggests that the production of relativistic ejecta is the key physical distinction between GRBs or XRFs and ordinary supernovae, while the nature of the central engine (black hole or magnetar) may distinguish typical bursts from low-luminosity, spherical events like XRF 060218.
Journal Article
Best Prices
This paper proposes a method for aggregating prices when retailers use periodic sales to price-discriminate amongst heterogeneous customers. In the motivating model, loyal customers buy one brand and do not strategically time purchases, while Bargain Hunters always pay the lowest price available, the “best price.” In the model, the best price is part of an exact price index. Accounting for the best price also substantially improves the empirical match between conventional price aggregation strategies and actual prices paid by consumers. The methodology improves inflation measurement while imposing little burden on the data-collection agency.
Journal Article
Nursing home staff networks and COVID-19
Nursing homes and other long-term care facilities account for a disproportionate share of COVID-19 cases and fatalities worldwide. Outbreaks in US nursing homes have persisted despite nationwide visitor restrictions beginning in mid-March. An early report issued by the Centers for Disease Control and Prevention identified staff members working in multiple nursing homes as a likely source of spread from the Life Care Center in Kirkland, WA, to other skilled nursing facilities. The full extent of staff connections between nursing homes—and the role these connections serve in spreading a highly contagious respiratory infection—is currently unknown given the lack of centralized data on cross-facility employment. We perform a large-scale analysis of nursing home connections via shared staff and contractors using device-level geolocation data from 50 million smartphones, and find that 5.1% of smartphone users who visited a nursing home for at least 1 h also visited another facility during our 11-wk study period—even after visitor restrictions were imposed. We construct network measures of connectedness and estimate that nursing homes, on average, share connections with 7.1 other facilities. Traditional federal regulatory metrics of nursing home quality are unimportant in predicting outbreaks, consistent with recent research. Controlling for demographic and other factors, a home’s staff network connections and its centrality within the greater network strongly predict COVID-19 cases.
Journal Article