Browsing by Author "Luo, X"

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Open Access
Assessing the Risks and Opportunities of Participation in Global Value Chains
(Achieving Workers’ Rights in the Global Economy, 2016-05-10) Gereffi, G; Luo, X
Open Access
Illposedness of C² Vortex Patches
(Archive for Rational Mechanics and Analysis, 2023-06-01) Kiselev, A; Luo, X
It is well known that vortex patches are wellposed in C1,α if 0 < α< 1 . In this paper, we prove the illposedness of C2 vortex patches. The setup is to consider the vortex patches in Sobolev spaces W2,p where the curvature of the boundary is Lp integrable. In this setting, we show the persistence of W2,p regularity when 1 < p< ∞ and construct C2 initial patch data for which the curvature of the patch boundary becomes unbounded immediately for t> 0 , though it regains C2 regularity precisely at all integer times without being time periodic. The key ingredient is the evolution equation for the curvature, the dominant term in which turns out to be linear and dispersive.
Open Access
Immunodominant liver-specific expression suppresses transgene-directed immune responses in murine pompe disease.
(Hum Gene Ther, 2012-05) Zhang, P; Sun, B; Osada, T; Rodriguiz, R; Yang, XY; Luo, X; Kemper, AR; Clay, TM; Koeberl, DD
Pompe disease can be treated effectively, if immune tolerance to enzyme replacement therapy (ERT) with acid α-glucosidase (GAA) is present. An adeno-associated viral (AAV) vector carrying a liver-specific regulatory cassette to drive GAA expression (AAV-LSPhGAA) established immune tolerance in GAA knockout (KO) mice, whereas ubiquitous expression with AAV-CBhGAA provoked immune responses. Therefore, we investigated the hypothesis that immune tolerance induced by hepatic-restricted expression was dominant. AAV-LSPhGAA and AAV-CBhGAA were administered singly or in combination to groups of adult GAA-KO mice, and AAV-LSPhGAA induced immune tolerance even in combination with AAV-CBhGAA. The dual vector approach to GAA expression improved biochemical correction of GAA deficiency and glycogen accumulations at 18 weeks, and improved motor function testing including wire-hang and grip-strength testing. The greatest efficacy was demonstrated by dual vector administration, when both vectors were pseudotyped as AAV8. T cells from mice injected with AAV-LSPhGAA failed to proliferate at all after an immune challenge with GAA and adjuvant, whereas mock-treated GAA-KO mice mounted vigorous T cell proliferation. Unlike AAV-LSPhGAA, AAV-CBhGAA induced selective cytokine and chemokine expression in liver and spleen after the immune challenge. AAV-CBhGAA transduced dendritic cells and expressed high-level GAA, whereas AAV-LSPhGAA failed to express GAA in dendritic cells. The level of transduction in liver was much higher after dual AAV8 vector administration at 18 weeks, in comparison with either vector alone. Dual vector administration failed to provoke antibody formation in response to GAA expression with AAV-CBhGAA; however, hepatic-restricted expression from dual vector expression did not prevent antibody formation after a strong immune challenge with GAA and adjuvant. The relevance of immune tolerance to gene therapy in Pompe disease indicates that hepatic expression might best be combined with nonhepatic expression, achieving the benefits of ubiquitous expression in addition to evading deleterious immune responses.
Open Access
Last Millennium ENSO Diversity and North American Teleconnections: New Insights From Paleoclimate Data Assimilation
(Paleoceanography and Paleoclimatology, 2022-03-01) Luo, X; Dee, S; Stevenson, S; Okumura, Y; Steiger, N; Parsons, L
El Niño-Southern Oscillation (ENSO) variability affects year-to-year changes in North American hydroclimate. Extra-tropical teleconnections are not always consistent between El Niño events due to stochastic atmospheric variability and diverse sea surface temperature anomalies, making it difficult to quantify teleconnections using only instrumentally-based records. Here we use two paleoclimate data assimilation (DA) products spanning the Last Millennium (LM) to compare changes in amplitudes and frequencies of diverse El Niño events during the pre-industrial period and 20th century, and to assess the stationarity of their North American hydroclimate impacts on multi-decadal to centennial timescales. Using several definitions for Central Pacific (CP) and Eastern Pacific (EP) El Niño, we find a marked increase in 20th century EP El Niño intensity, but no significant changes in CP or EP El Niño frequencies in response to anthropogenic forcing. The associated hydroclimate anomalies indicate (a) dry conditions across the eastern-central and northwestern U.S. during CP El Niño and wetter conditions in the same regions during EP El Niño; (b) wet conditions over the southwestern U.S. for both El Niño types. The magnitude of regional hydroclimate teleconnections also shows large natural variability on multi-decadal to centennial timescales. However, when the entire LM is considered, mean hydroclimate anomalies in North America during CP or EP El Niño are consistent in terms of sign (wet vs. dry). Results are sensitive to proxy data and model priors used in DA products. Inconsistencies between El Niño classification methods underscore the need for improved ENSO diversity classification when assessing precipitation teleconnections.
Open Access
The α-SQG patch problem is illposed in C^2,β and W^2,p
(Communications on Pure and Applied Mathematics, 2024-01-01) Kiselev, A; Luo, X
We consider the patch problem for the α-(surface quasi-geostrophic) SQG system with the values α = 0 and (Formula presented.) being the 2D Euler and the SQG equations respectively. It is well-known that the Euler patches are globally wellposed in non-endpoint C2,β Hölder spaces, as well as in W2,p, (Formula presented.) spaces. In stark contrast to the Euler case, we prove that for (Formula presented.), the (Formula presented.) -SQG patch problem is strongly illposed in every (Formula presented.) Hölder space with (Formula presented.). Moreover, in a suitable range of regularity, the same strong illposedness holds for every W2,p Sobolev space unless p = 2.