29 research outputs found
Read-only Prompt Optimization for Vision-Language Few-shot Learning
In recent years, prompt tuning has proven effective in adapting pre-trained
vision-language models to downstream tasks. These methods aim to adapt the
pre-trained models by introducing learnable prompts while keeping pre-trained
weights frozen. However, learnable prompts can affect the internal
representation within the self-attention module, which may negatively impact
performance variance and generalization, especially in data-deficient settings.
To address these issues, we propose a novel approach, Read-only Prompt
Optimization (RPO). RPO leverages masked attention to prevent the internal
representation shift in the pre-trained model. Further, to facilitate the
optimization of RPO, the read-only prompts are initialized based on special
tokens of the pre-trained model. Our extensive experiments demonstrate that RPO
outperforms CLIP and CoCoOp in base-to-new generalization and domain
generalization while displaying better robustness. Also, the proposed method
achieves better generalization on extremely data-deficient settings, while
improving parameter efficiency and computational overhead. Code is available at
https://github.com/mlvlab/RPO.Comment: Accepted at ICCV202
How chip size impacts steam pretreatment effectiveness for biological conversion of poplar wood into fermentable sugars
Background Woody biomass is highly recalcitrant to enzymatic sugar release and often requires significant size reduction and severe pretreatments to achieve economically viable sugar yields in biological production of sustainable fuels and chemicals. However, because mechanical size reduction of woody biomass can consume significant amounts of energy, it is desirable to minimize size reduction and instead pretreat larger wood chips prior to biological conversion. To date, however, most laboratory research has been performed on materials that are significantly smaller than applicable in a commercial setting. As a result, there is a limited understanding of the effects that larger biomass particle size has on the effectiveness of steam explosion pretreatment and subsequent enzymatic hydrolysis of wood chips. Results To address these concerns, novel downscaled analysis and high throughput pretreatment and hydrolysis (HTPH) were applied to examine whether differences exist in the composition and digestibility within a single pretreated wood chip due to heterogeneous pretreatment across its thickness. Heat transfer modeling, Simonsâ stain testing, magnetic resonance imaging (MRI), and scanning electron microscopy (SEM) were applied to probe the effects of pretreatment within and between pretreated wood samples to shed light on potential causes of variation, pointing to enzyme accessibility (i.e., pore size) distribution being a key factor dictating enzyme digestibility in these samples. Application of these techniques demonstrated that the effectiveness of pretreatment of Populus tremuloides can vary substantially over the chip thickness at short pretreatment times, resulting in spatial digestibility effects and overall lower sugar yields in subsequent enzymatic hydrolysis. Conclusions These results indicate that rapid decompression pretreatments (e.g., steam explosion) that specifically alter accessibility at lower temperature conditions are well suited for larger wood chips due to the non-uniformity in temperature and digestibility profiles that can result from high temperature and short pretreatment times. Furthermore, this study also demonstrated that wood chips were hydrated primarily through the natural pore structure during pretreatment, suggesting that preserving the natural grain and transport systems in wood during storage and chipping processes could likely promote pretreatment efficacy and uniformity
Vortex wandering in a forest of splayed columnar defects
We investigate the scaling properties of single flux lines in a random
pinning landscape consisting of splayed columnar defects. Such correlated
defects can be injected into Type II superconductors by inducing nuclear
fission or via direct heavy ion irradiation. The result is often very efficient
pinning of the vortices which gives, e.g., a strongly enhanced critical
current. The wandering exponent \zeta and the free energy exponent \omega of a
single flux line in such a disordered environment are obtained analytically
from scaling arguments combined with extreme-value statistics. In contrast to
the case of point disorder, where these exponents are universal, we find a
dependence of the exponents on details in the probability distribution of the
low lying energies of the columnar defects. The analytical results show
excellent agreement with numerical transfer matrix calculations in two and
three dimensions.Comment: 11 pages, 9 figure
Quantum heuristic algorithm for traveling salesman problem
We propose a quantum heuristic algorithm to solve a traveling salesman
problem by generalizing Grover search. Sufficient conditions are derived to
greatly enhance the probability of finding the tours with extremal costs,
reaching almost to unity and they are shown characterized by statistical
properties of tour costs. In particular for a Gaussian distribution of the
tours along the cost we show that the quantum algorithm exhibits the quadratic
speedup of its classical counterpart, similarly to Grover search.Comment: Published versio
How chip size impacts steam pretreatment effectiveness for biological conversion of poplar wood into fermentable sugars
BACKGROUND: Woody biomass is highly recalcitrant to enzymatic sugar release and often requires significant size reduction and severe pretreatments to achieve economically viable sugar yields in biological production of sustainable fuels and chemicals. However, because mechanical size reduction of woody biomass can consume significant amounts of energy, it is desirable to minimize size reduction and instead pretreat larger wood chips prior to biological conversion. To date, however, most laboratory research has been performed on materials that are significantly smaller than applicable in a commercial setting. As a result, there is a limited understanding of the effects that larger biomass particle size has on the effectiveness of steam explosion pretreatment and subsequent enzymatic hydrolysis of wood chips. RESULTS: To address these concerns, novel downscaled analysis and high throughput pretreatment and hydrolysis (HTPH) were applied to examine whether differences exist in the composition and digestibility within a single pretreated wood chip due to heterogeneous pretreatment across its thickness. Heat transfer modeling, Simonsâ stain testing, magnetic resonance imaging (MRI), and scanning electron microscopy (SEM) were applied to probe the effects of pretreatment within and between pretreated wood samples to shed light on potential causes of variation, pointing to enzyme accessibility (i.e., pore size) distribution being a key factor dictating enzyme digestibility in these samples. Application of these techniques demonstrated that the effectiveness of pretreatment of Populus tremuloides can vary substantially over the chip thickness at short pretreatment times, resulting in spatial digestibility effects and overall lower sugar yields in subsequent enzymatic hydrolysis. CONCLUSIONS: These results indicate that rapid decompression pretreatments (e.g., steam explosion) that specifically alter accessibility at lower temperature conditions are well suited for larger wood chips due to the non-uniformity in temperature and digestibility profiles that can result from high temperature and short pretreatment times. Furthermore, this study also demonstrated that wood chips were hydrated primarily through the natural pore structure during pretreatment, suggesting that preserving the natural grain and transport systems in wood during storage and chipping processes could likely promote pretreatment efficacy and uniformity
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Topochemical Understanding of Lignin Distribution During Hydrothermal Flowthrough Pretreatment
Surface Characterization of <i>Populus</i> during <i>Caldicellulosiruptor bescii</i> Growth by TOF-SIMS Analysis
<i>Caldicellulosiruptor bescii</i> is a thermophilic,
anaerobic bacterium that is capable of utilizing unpretreated biomass
in addition to breaking down cellulose and hemicellulose into simple
sugars. Despite the fact that <i>C. bescii</i> must first
bind to the surface of the biomass, there has been no analysis of
the morphological or chemical changes to the biomass surface as a
result of incubation with the micro-organism. To understand more about <i>C. bescii</i> growth, juvenile poplar stems were sectioned (80
ÎŒm thick) and incubated with <i>C. bescii</i> beyond
the typical 24 h experiment length. Monitoring the cell counts during
incubation revealed a biphasic growth pattern. The impact the micro-organism
had on the surface was determined by scanning electron microscopy
(SEM) and time-of-flight secondary ion mass spectrometry (ToF-SIMS),
which showed physical crevices in the cell wall caused by the <i>C. bescii</i> along with a decrease of polysaccharide ions and
an increase in lignin ions on the poplar surface. Employing infrared
microspectroscopy, the decreasing trend was corroborated