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Certain semiconductor structures, so-called quantum dots, might constitute the foundation of quantum communication. They are an efficient interface between matter and light, with photons (light particles) emitted by the quantum dots transporting information across large distances. However, structures form by default during the manufacture of quantum dots that interfere with communication. Researchers at the University of Basel, Ruhr-Universität Bochum, and Forschungszentrum Jülich have now successfully eliminated these interferences. They’ve published their report in the journal Communications Physics from 9 August 2019.

Light particles capable of transporting information across large distances

Quantum dots can be realised in semiconductors if researchers lock an electron and an electron hole — i.e. a positive charge at a position where an electron should exist — in a constricted space. Together, electron and electron hole form an excited state. When they recombine, the excited state disappears and a photon is generated. “That photon might be usable as information carrier in quantum communication across large distances,” says Dr. Arne Ludwig from the Chair for Applied Solid State Physics in Bochum.

The quantum dots manufactured in Bochum are generated in the semiconductor material indium arsenide. The researchers grow the material on a gallium arsenide substrate. In the process, a smooth indium arsenide layer forms at a thickness of a mere one and a half atomic layers — the so-called wetting layer. Subsequently, the researchers generate small islands with a diameter of 30 nanometres and a height of a few nanometres. These are the quantum dots.

Interfering photons from wetting layer

The wetting layer that has to be deposited in the first step causes problems, because it, too, contains excited electron hole states that decay and may release photons. In the wetting layer, these states decay even more easily than in the quantum dots. The photons emitted in the process can’t be used in quantum communication, however; rather, they generate a static noise in the system.

“The wetting layer covers the entire surface while the quantum dots only cover a thousandth of the semiconductor chip, which is why the interfering light is approximately a thousand times stronger than the light emitted by the quantum dots,” explains Andreas Wieck, Head of the Chair for Applied Solid State Physics in Bochum. “The wetting layer radiates photons at a slightly higher frequency and at a much higher intensity than the quantum dots. It’s as if the quantum dots emitted the chamber pitch A, whereas the wetting layer emitted an B that was a thousand times louder.”

Additional layer eliminates interferences

“We have been able to ignore those interferences by exciting only the required energy states,” says Matthias Löbl from the University of Basel. “However, if quantum dots are to be used as information units for quantum applications, it might be ideal to charge them with more electrons. But in that case, the energy levels in the wetting layer would be likewise excited,” adds Arne Ludwig.

The research team has now eliminated this interference by adding an aluminium arsenide layer grown above the quantum dots in the wetting layer. The energy states in the wetting layer are thus removed, which, in turn, makes it less likely for electrons and electron holes to recombine and emit photons.

Collaboration between three research institutes

The samples for the current project were generated by Dr. Sven Scholz at the RUB Chair of Applied Solid State Physics, whose work was awarded with the dissertation prize by the Wilhelm and Else Heraeus Foundation in June 2019. The measurements of the size of interferences with and without the aluminium arsenide layer were conducted by the team at the University of Basel, under the auspices of Matthias Löbl, Dr. Immo Söllner and Professor Richard Warburton. The group at Forschungszentrum Jülich captured high-resolution microscope images of the samples.

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Materials provided by Ruhr-University Bochum. Original written by Julia Weiler; translated by Donata Zuber. Note: Content may be edited for style and length.

Researchers found no evidence that those with MCI would derive less benefit from evidence-based treatment that’s offered to their cognitively normal peers who have heart attacks, says lead author Deborah Levine, M.D., MPH.

“Patients should get the treatments they would want if they were properly informed,” says Levine, an associate professor of internal medicine and neurology at Michigan Medicine, the academic medical center of the University of Michigan.

Some people with thinking, memory and language problems have MCI. Unlike dementia, which severely interferes with daily functioning and worsens over time, MCI does not severely interfere with daily functioning and might not worsen over time. Although people with MCI have an increased risk of developing dementia, it’s not an inevitable next step, Levine says.

“While some may progress to dementia, many will persist in having MCI, and a few will actually improve and revert to normal cognition,” says Levine, also a member of the University of Michigan Institute for Healthcare Policy and Innovation. “Many older adults with MCI live years with good quality of life, and so face common health risks of aging like heart attack and stroke.

“Clinicians, patients and families might be overestimating the risk of dementia after a mild cognitive impairment diagnosis even without realizing it. These older adults with MCI should still receive evidence-based treatments when indicated.”

The research, published in the Journal of General Internal Medicine, found pre-existing MCI was associated with significantly lower use of guideline-concordant care after a heart attack, whether catheter-based or open surgery. The study measured 609 adults ages 65 and older who were hospitalized for a heart attack between 2000 and 2011.

Levine notes both cardiac catheterization (35% less likely in patients with pre-existing MCI) and coronary revascularization (45% less likely in patients with pre-existing MCI) have been shown to be highly effective at reducing deaths and improving physical functioning after heart attack in multiple large clinical trials.

‘A timely issue’

Physicians must weigh the competing risks of all health problems that increase with age, Levine says, including heart disease and cognitive decline. Many families are dealing with both concerns at once in their older loved ones.

“This is a timely issue because as the population ages, the number of seniors 85 years old and older has become the fastest-growing segment of the U.S. population,” Levine says. “Seniors 85 and older are most likely to have MCI, and their incidence of heart attack has surged.”

However, cardiovascular disease, including heart attack and stroke, is still the leading cause of death and serious morbidity in older adults, whether they have MCI or normal cognitive functioning.

Up to 1 in 5 adults ages 65 and older has MCI, although many may be undiagnosed, Levine says. Since the Affordable Care Act mandated coverage of cognitive impairment assessments for Medicare beneficiaries, MCI diagnoses are expected to increase, she adds.

The need to question decision-making

Although much recent medical literature addresses overtreatment, Levine says this research shows undertreatment with high-value therapies can also be a problem.

Her team’s ongoing research finds physicians might not be recommending invasive treatments as often after an older patient with some memory and thinking problems has a heart attack. She encourages clinicians to reflect on the influence of MCI in their decision-making.

“It’s important for providers to consider whether they are recommending against treating a patient just because they have MCI,” Levine says. “Physicians can think about offering treatments to all patients when clinically indicated.”

Invasive treatments may not be indicated in those with advanced dementia or a limited life expectancy, she says, but MCI does not fall in that category.

This potential disconnect in provider recommendations provides an opportunity for patients and families to empower themselves by having conversations about the care they’d want if they become ill, she says. People with MCI can still participate in these types of discussions, and families don’t need to wait until an event happens to start the conversation.

“In these discussions, patients and families often think about catastrophic illnesses where life support measures may be used, but heart attacks and stroke are much more common, and they’re treatable,” Levine says.

“Because dementia is so feared among older adults and their families, it’s understandable and appropriate that it may weigh heavily on the decisions for all types of care, including heart attack care,” adds co-author Kenneth Langa, M.D., Ph.D., a professor of internal medicine at Michigan Medicine and a member of the Institute for Healthcare Policy and Innovation. “Our study emphasizes the importance of differentiating between MCI and dementia and of educating patients, families and clinicians on the relative risks of further cognitive decline versus common cardiovascular conditions for people with MCI.”

An ongoing effort

Levine and colleagues used data from the Health and Retirement Study, a nationally representative longitudinal study of older Americans that’s based at U-M.

Heart attack, or acute myocardial infarction, was an appealing lens to research whether patients with MCI receive guideline-based treatment, Levine says. Heart attacks are acute, emergent medical problems that are common in seniors and have robust evidence of effective treatment, she adds.

Levine’s team is also studying the effect of pre-existing MCI on treatment for acute ischemic stroke, and the reasons physician recommendations and patient preferences for effective treatment after stroke or heart attack might be different if the patient already has MCI.

“Studies like this are an important first step in raising awareness on MCI so that providers, like cardiologists, can make sure they offer the best therapies available during heart attacks,” says senior author Brahmajee Nallamothu, M.D., MPH, an interventional cardiologist and professor of internal medicine at Michigan Medicine.

Parasites, such as viruses, insects, helminths, and bacteria, seek to manipulate host behavior for numerous reasons. Parasitic organisms may induce behavioral changes in order to increase their chances of transmission from one host to another. In a similar vein, parasites may disrupt a host’s normal neural functioning to prompt the organism to travel to an environment that is more hospitable for the parasite or more conducive for reproduction. Host bodies are sometimes co-opted and utilized as safe environments for the development of the parasite’s offspring.

The means by which parasites attempt to alter host behavior also vary. Parasites may use an immunological approach by disrupting responses in an organism’s immune system. A more direct option may be to employ neuropharmacological manipulation by secreting substances that interfere with the host’s neurotransmitters. Parasites may also take the genomic/proteomic route by changing gene expression.

Expanding beyond the motivations and tactics of parasites, Del Giudice posits that attacks from these biochemical mechanisms place significant pressure on the nervous system to adapt and develop countermeasures. Drawing upon previous literature and real-world examples, the article proposes four categories of potential host countermeasures. Analyzing this taxonomy, Del Giudice argues that when encountering manipulation, hosts may prevent parasites from bypassing the brain’s protective barrier, force parasites to work harder and release greater amounts of neuroactive substances, make signals more complex, or strengthen the brain’s ability to endure disturbances.

Elaborating further on these countermeasures, the author considers the potential evolutionary constraints and the associated “robustness-fragility tradeoffs.” Although countermeasures may increase complexity and deter parasites, new adaptations may simultaneously weaken another section of the system and provide alternative targets for parasites.

Taking into account the proposed effectiveness of the mechanisms discussed, the article suggests studying host-parasite interactions could aid in furthering neuroscience and psychopharmacology research. By studying adaptations to parasitic attacks, neuroscientists could gain additional perspective into how continuous evolutionary battles produce inefficiency or how once-critical mechanisms over time serve unrelated functions. In psychopharmacology, the biochemical methods parasites use mimic those of pharmacological drugs. Researchers could analyze the ways brain structures reject pharmacological interventions by parasites and, in turn, use that information to make psychoactive drugs more effective for patients.

“The unrelenting pressure exerted by parasites must have shaped the evolution of nervous and endocrine systems at all levels, with important consequences even for animals that are not (or no longer) manipulation targets. If this is true, many aspects of neurobiology are destined to remain mysterious or poorly understood until parasites — the brain’s invisible designers — are finally included in the picture,” Del Giudice writes.

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Materials provided by University of Chicago Press Journals. Note: Content may be edited for style and length.

Among scientists, there are two camps of thought. First is that animals use local cues within their vicinity to determine where to migrate. Animals might move up to areas with greener forage — often termed green-wave surfing — or move down from mountains with deeper snow. The second idea is that animals develop memory of the landscape where they live and then use that information to guide their movements.

Recent research from the University of Wyoming has found that memory explains much of deer behavior during migration: Mule deer navigate in spring and fall mostly by using their knowledge of past migration routes and seasonal ranges.

The study found that the location of past years’ migratory route and summer range had 2-28 times more influence on a deer’s choice of a migration path than environmental factors such as tracking spring green-up, autumn snow depth or topography.

“These animals appear to have a cognitive map of their migration routes and seasonal ranges, which helps them navigate tens to hundreds of miles between seasonal ranges,” says the lead author of the paper, Jerod Merkle, assistant professor and Knobloch Professor in Migration Ecology and Conservation in the Department of Zoology and Physiology at UW.

The findings recently were published in Ecology Letters, a leading journal within the field of ecology. Co-authors of the paper included Hall Sawyer, with Western EcoSystems Technology Inc.; Kevin Monteith and Samantha Dwinnell, with UW’s Haub School of Environment and Natural Resources; Matthew Kauffman, with the U.S. Geological Survey Wyoming Cooperative Fish and Wildlife Research Unit at UW; and Gary Fralick, with the Wyoming Game and Fish Department.

Scientists had long presumed that migratory behavior was dictated by availability of food resources and other external factors. Where you find resources, you will find species that exploit them, the theory went.

The UW team found it is not that simple. Without the intrinsic factor of landscape memory to guide deer between seasonal ranges, the long-distance corridors of western Wyoming’s Green River Basin, for example — exceeding 300 miles round-trip in some cases — would not exist in their present form.

“It appears that green-wave surfing helps them determine when to move within a kind of ‘map’ in their brain,” Merkle says. “The timing of spring green-up determines when an animal should migrate, but spatial memory determines where to migrate.”

The finding has important conservation implications. Because landscape memory so strongly underlies mule deer migratory behavior, the loss of a migratory population also will destroy the herd’s collective mental map of how to move within a landscape, making it very difficult to restore lost migration routes. Patches of potential habitat likely will go unused.

“This is yet another study that makes clear that animals must learn and remember how to make these incredible journeys,” say Kauffman, who leads the Wyoming Cooperative Fish and Wildlife Research Unit, where the research was conducted. “This is critical for conservation, because it tells us that, to conserve a migration corridor, we need to conserve the specific animals who have the knowledge necessary to make the journey.”

The study bolsters the findings of a 2018 paper in the journal Science by a UW-led team that found translocated bighorn sheep and moose with no knowledge of the landscape can take anywhere from several decades to a century to learn how to migrate to vacant habitats.

Similarly, strategies such as off-site restoration or mitigation may be unsuccessful if restored habitats are not “discovered” and integrated into the memory of individuals.

The study further makes a case that biologists will not be able to successfully predict migration corridors — or optimally manage populations — based on environmental information or range quality alone. Managers will find it difficult to evaluate potential conservation actions without directly gathering movement data, crucial information that reveals the migration knowledge that animals carry around in their heads.

Moreover, the research shows that migrants can obtain greater forage benefits during spring migration using memory of a vast landscape, compared to migrants that rely simply on foraging cues in their local area.

This suggests that the migratory routes we see today are optimized across generations for green-wave surfing in large landscapes. These learned migration corridors are not readily discoverable by animals if they cannot access the memories established by past generations.