2,125 research outputs found
Influence of ultrafiltration membrane characteristics on adsorptive fouling with dextrans
This paper presents a detailed investigation of fouling mechanisms for ultrafiltration membranes with polysaccharides obtained by studying
membrane–solute (static adsorption) and membrane–solute–solute interactions (ultrafiltration (UF)). Two polyethersulfone (PES) membranes
and one stabilized cellulose (cellulosic) membrane with a nominal cut-off of 10 kg/mol and dextrans with average molar mass (M) of 4,
10 and 15 kg/mol were used. The membranes before and after static adsorption of dextran were characterized by captive bubble contact
angle and tangential streaming potential measurements as well as ultrafiltration sieving curves for polyethylene glycols. Significant water
flux reductions (4–15%), which also correlated with dextran molar mass, and changes of the other membrane characteristics occurred after
static dextran adsorption for the PES membranes. An empirical model to describe the correlation between the relative water flux reduction
and the concentration of solute had also been proposed. In contrast, no significant changes could be detected for the cellulosic membrane.
Significant membrane–solute interactions had also been confirmed in the ultrafiltration experiments with dextrans where irreversible fouling
had been observed for the PES but not for the cellulosic membranes. The results provide fundamental information for a better understanding
of fouling by polysaccharides. In particular, it had been confirmed that hydrophilic and neutral dextrans can significantly foul PES membranes
via adsorption to the surface of the membrane polymer. On this basis, methods for control of this fouling can be properly developed
Non-interferometric Test of Collapse Models in Optomechanical Systems
The test of modifications to quantum mechanics aimed at identifying the
fundamental reasons behind the un-observability of quantum mechanical
superpositions at the macro-scale is a crucial goal of modern quantum
mechanics. Within the context of collapse models, current proposals based on
interferometric techniques for their falsification are far from the
experimental state-of-the-art. Here we discuss an alternative approach to the
testing of quantum collapse models that, by bypassing the need for the
preparation of quantum superposition states might help us addressing non-linear
stochastic mechanisms such as the one at the basis of the continuous
spontaneous localisation model.Comment: 6 pages, accepted for publication in Phys. Rev. Lett.
Latent Variable Approaches for Understanding Heterogeneity in Depression: A Dissertation
Background: Major depression is one of the most prevalent, disabling, and costly illnesses worldwide. Despite a 400% increase in antidepressant medication use since 1988, fewer than half of treated depression patients experience a clinically meaningful reduction in symptoms and uncertainty exists regarding how to successfully obtain symptom remission. Identifying homogenous subgroups based on clinically observable characteristics could improve the ability to efficiently predict who will benefit from which treatments.
Methods: Latent class analysis and latent transition analysis (LTA) were applied to data from the Sequenced Treatment Alternatives to Relieve Depression (STAR*D) study to explore how to efficiently identify subgroups comprised of the multiple dimensions of depression and examine changes in subgroup membership during treatment. The specific aims of this dissertation were to: 1) evaluate latent depression subgroups for men and women prior to antidepressant treatment; 2) examine transitions in these subgroups over 12 weeks of citalopram treatment; and 3) examine differences in functional impairment between women’s depression subgroups throughout treatment.
Results: Four subgroups of depression were identified for men and women throughout this work. Men’s subgroups were distinguished by depression severity and psychomotor agitation and retardation. Severity, appetite changes, insomnia, and psychomotor disturbances characterized women’s subgroups. Psychiatric comorbidities, especially anxiety disorders, were related to increased odds of membership in baseline moderate and severe depression subgroups for men and women. After 12 weeks of citalopram treatment, depression severity and psychomotor agitation were related to men’s chances of improving. Severity and appetite changes were related to women’s likelihood of improving during treatment. When functional impairment was incorporated in LTA models for women, baseline functional impairment levels were related to both depression subgroups at baseline and chances of moving to a different depression subgroup after treatment.
Conclusion: Depression severity, psychomotor disturbances, appetite changes, and insomnia distinguished depression subgroups in STAR*D. Gender, functional impairment, comorbid psychiatric disorders, and likelihood of transitioning to subgroups characterized by symptom improvement differed between these subgroups. The results of this work highlight how relying solely on summary symptom rating scale scores during treatment obscures changes in depression that might be informative for improving treatment response
Testing collapse models with levitated nanoparticles: the detection challenge
We consider a nanoparticle levitated in a Paul trap in ultrahigh cryogenic
vacuum, and look for the conditions which allow for a stringent
noninterferometric test of spontaneous collapse models. In particular we
compare different possible techniques to detect the particle motion. Key
conditions which need to be achieved are extremely low residual pressure and
the ability to detect the particle at ultralow power. We compare three
different detection approaches based respectively on a optical cavity, optical
tweezer and a electrical readout, and for each one we assess advantages,
drawbacks and technical challenges
Tracking spin and charge with spectroscopy in spin-polarised 1D systems
We calculate the spectral function of a one-dimensional strongly interacting
chain of fermions, where the response can be well understood in terms of spinon
and holon excitations. Upon increasing the spin imbalance between the spin
species, we observe the single-electron response of the fully polarised system
to emanate from the holon peak while the spinon response vanishes. For
experimental setups that probe one-dimensional properties, we propose this
method as an additional generic tool to aid the identification of spectral
structures, e.g. in ARPES measurements. We show that this applies even to
trapped systems having cold atomic gas experiments in mind.Comment: 5 pages, 4 figure
Detection of deep-subwavelength dielectric layers at terahertz frequencies using semiconductor plasmonic resonators
Plasmonic bowtie antennas made of doped silicon can operate as plasmonic
resonators at terahertz (THz) frequencies and provide large field enhancement
close to their gap. We demonstrate both experimentally and theoretically that
the field confinement close to the surface of the antenna enables the detection
of ultrathin (100 nm) inorganic films, about 3750 times thinner than the free
space wavelength. Based on model calculations, we conclude that the detection
sensitivity and its variation with the thickness of the deposited layer are
related to both the decay of the local THz field profile around the antenna and
the local field enhancement in the gap of the bowtie antenna. This large field
enhancement has the potential to improve the detection limits of plasmon-based
biological and chemical sensors
Testing the gravitational field generated by a quantum superposition
What gravitational field is generated by a massive quantum system in a spatial superposition? Despite decades of intensive theoretical and experimental research, we still do not know the answer. On the experimental side, the difficulty lies in the fact that gravity is weak and requires large masses to be detectable. However, it becomes increasingly difficult to generate spatial quantum superpositions for increasingly large masses, in light of the stronger environmental effects on such systems. Clearly, a delicate balance between the need for strong gravitational effects and weak decoherence should be found. We show that such a trade off could be achieved in an optomechanics scenario that allows to witness whether the gravitational field generated by a quantum system in a spatial superposition is in a coherent superposition or not. We estimate the magnitude of the effect and show that it offers perspectives for observability
Testing the gravitational field generated by a quantum superposition
What gravitational field is generated by a massive quantum system in a spatial superposition? Despite decades of intensive theoretical and experimental research, we still do not know the answer. On the experimental side, the difficulty lies in the fact that gravity is weak and requires large masses to be detectable. However, it becomes increasingly difficult to generate spatial quantum superpositions for increasingly large masses, in light of the stronger environmental effects on such systems. Clearly, a delicate balance between the need for strong gravitational effects and weak decoherence should be found. We show that such a trade off could be achieved in an optomechanics scenario that allows to witness whether the gravitational field generated by a quantum system in a spatial superposition is in a coherent superposition or not. We estimate the magnitude of the effect and show that it offers perspectives for observability
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