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Undecidability and Quantum Mechanics
Recently, great attention has been devoted to the problem of the undecidability of specific questions in quantum mechanics. In this context, it has been shown that the problem of the existence of a spectral gap, i.e., energy difference between the ground state and the first excited state, is algorithmically undecidable. Using this result herein proves that the existence of a quantum phase transition, as inferred from specific microscopic approaches, is an undecidable problem, too. Indeed, some methods, usually adopted to study quantum phase transitions, rely on the existence of a spectral gap. Since there exists no algorithm to determine whether an arbitrary quantum model is gapped or gapless, and there exist models for which the presence or absence of a spectral gap is independent of the axioms of mathematics, it infers that the existence of quantum phase transitions is an undecidable problem. 
  • 1.3K
  • 18 Oct 2022
Topic Review
Uncrewed Aerial Vehicles in Bridge Inspection
Uncrewed Aerial Vehicles (UAV) constitute a rapidly evolving technology field that is becoming more accessible and capable of supplementing, expanding, and even replacing some traditionally manual bridge inspections. Given the classification of the bridge inspection types as initial, routine, in-depth, damage, special, and fracture critical members, specific UAV mission requirements can be developed, and their suitability for UAV application examined.
  • 598
  • 06 Apr 2022
Topic Review
Uncovering the Tumor Antigen Landscape
According to the latest available data, cancer is the second leading cause of death, highlighting the need for novel cancer therapeutic approaches. In this context, immunotherapy is emerging as a reliable first-line treatment for many cancers, particularly metastatic melanoma. Indeed, cancer immunotherapy has attracted great interest following the recent clinical approval of antibodies targeting immune checkpoint molecules, such as PD-1, PD-L1, and CTLA-4, that release the brakes of the immune system, thus reviving a field otherwise poorly explored. Cancer immunotherapy mainly relies on the generation and stimulation of cytotoxic CD8 T lymphocytes (CTLs) within the tumor microenvironment (TME), priming T cells and establishing efficient and durable anti-tumor immunity. Therefore, there is a clear need to define and identify immunogenic T cell epitopes to use in therapeutic cancer vaccines. Naturally presented antigens in the human leucocyte antigen-1 (HLA-I) complex on the tumor surface are the main protagonists in evocating a specific anti-tumor CD8+ T cell response. However, the methodologies for their identification have been a major bottleneck for their reliable characterization. Consequently, the field of antigen discovery has yet to improve.
  • 962
  • 26 Oct 2020
Topic Review
Uncoupling Proteins for Neurodegenerative Diseases
Most of the major retinal degenerative diseases are associated with significant levels of oxidative stress. One of the major sources contributing to the overall level of stress is the reactive oxygen species (ROS) generated by mitochondria. The driving force for ROS production is the proton gradient across the inner mitochondrial membrane. This gradient can be modulated by members of the uncoupling protein family, particularly the widely expressed UCP2. The overexpression and knockout studies of UCP2 in mice have established the ability of this protein to provide neuroprotection in a number of animal models of neurological disease, including retinal diseases. The expression and activity of UCP2 are controlled at the transcriptional, translational and post-translational levels, making it an ideal candidate for therapeutic intervention. 
  • 698
  • 30 Jun 2022
Topic Review
Uncoupling Aging from Chronological Time
Cellular life evolved from simple unicellular organisms that could replicate indefinitely, being essentially ageless. At this point, life split into two fundamentally different cell types: the immortal germline representing an unbroken lineage of cell division with no intrinsic endpoint and the mortal soma, which ages and dies. We consider aging as a process not fixed to the pace of chronological time but one that can speed up or slow down depending on the rate of intrinsic cellular clocks. Moreover germline factor reprogramming might be used to slow the rate of aging and potentially reverse it by causing the clocks to tick backward. Therefore, reprogramming may eventually lead to therapeutic strategies to treat degenerative diseases by altering aging itself, the one condition common to us all.
  • 541
  • 02 May 2021
Topic Review
Unconventional Treatment of Biofilm Infection
Today, researchers are looking at new ways to treat severe infections caused by resistance to standard antibiotic therapy. This is quite challenging due to the complex and interdependent relationships involved: the cause of infection–the patient–antimicrobial agents. The sessile biofilm form is essential in research to reduce resistance to very severe infections (such as ESKAPE pathogens: Enterococcus faecium, Staphylococcus aureus, Klebsiella pneumoniae, Acinetobacter baumanni, Pseudomonas aeruginosa, and Enterobacter spp). The purpose of this study is to elucidate the mechanisms of the occurrence, maintenance, and suppression of biofilm infections. One form of biofilm suppression is the efficient action of natural antagonists of bacteria—bacteriophages. Bacteriophages effectively penetrate the biofilm’s causative cells. They infect those bacterial cells and either destroy them or prevent the infection from spreading. In this process, bacteriophages are specific, relatively easy to apply, and harmless to the patient. Antimicrobial peptides (AMPs) support the mechanisms of bacteriophages’ action. AMPs could also attack and destroy infectious agents on their own (even on biofilm). AMPs are simple, universal peptide molecules, mainly cationic peptides. Additional AMP research could help develop even more effective treatments of biofilm (bacteriophages, antibiotics, AMPs, nanoparticles). This is a review of recent unconventional agents, such as bacteriophages and AMPs, used for the eradication of biofilm, providing an overview of potentially new biofilm treatment strategies.
  • 737
  • 20 Oct 2020
Topic Review
Unconventional Tourism Services Based on Autonomous Vehicles
The spread of autonomous vehicles (AVs) could fundamentally change tourism-related mobility in the near future. However, the empirical research on tourism impacts is still very limited. 
  • 540
  • 31 Mar 2022
Topic Review
Unconventional Reservoirs
The world’s energy demand is steadily increasing where it has now become not easy for conventional hydrocarbon reservoirs to meet levels of demand. Therefore, oil and gas companies are seeking novel ways to exploit and unlock the potential of unconventional resources. Drilling of high-pressure high-temperature (HPHT) wells and shale reservoirs has become more widespread in the global petroleum and natural gas industry. There is a current need to extend robust techniques beyond costly drilling and completion jobs, with the potential for exponential expansion. This paper explains a better understanding of the selection of drilling fluids and additives for unconventional hydrocarbon reservoirs. 
  • 1.8K
  • 13 Jul 2020
Topic Review
Unconventional Outside Left-Turn Lanes
For countries driving right, left-turn lanes are usually on the inside of roads. However, when there are a large number of vehicles turning left in the outer lane of the upstream section of the intersection, these vehicles will be forced to pass many consecutive parallel lanes and then enter the left-turn lane. During this process, many traffic conflicts will occur between left-turning vehicles and going-straight vehicles, which will lead to longer traffic delays. 
  • 562
  • 15 Jul 2022
Topic Review
Uncontrolled Outdoor Access for Cats
Outdoor access for companion cats is a controversial topic. Some have suggested that outdoor access can negatively impact the welfare of companion cats through increased risks of disease and parasites, injury or death due to traffic, predation or ingestion of toxins, and becoming lost. In addition, cats can negatively influence their environments due to the predation of small birds and mammals, and they are sometimes a nuisance to human neighbors. Despite these concerns, recent estimates suggest that many owners still allow their cats outside, likely because it also provides cats with exercise, and allows them to perform natural behaviors, such as hunting, exploring, and climbing. While some suggest that cats need outdoor access, others recommend ways for cats to meet these needs indoors by providing enrichment and properly supervising cats during outdoor access. 
  • 533
  • 09 Dec 2021
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