A “significant breakthrough” in color switching for nanocrystals that unlocks exciting possibilities for a simple, energy-efficient display design and for tunable light sources for many technologies has been achieved by researchers at the Hebrew University of Jerusalem (HU).

Colored light and its tunability are the basis of many essential modern-day technologies from lighting and displays to fast optical fiber-communication networks. 

The discovery also has potential applications for sensitive sensors of various substances, including biological and neuroscience uses and advancements in quantum-communication technologies. This nanomaterial breakthrough holds the promise of inspiring exciting innovations in the future, the team said.

They published their findings in the prestigious journal Nature Materials under the title “Electric field induced color switching in colloidal quantum dot molecules at room temperature.” 

While nanocrystals offer color tunability and are used in various technologies, achieving a variety of colors requires using different nanocrystals for each color and dynamic switching between colors has not been possible. 

Overcoming nanocrystal tech barriers

A team at HU’s Institute of Chemistry and the Center for Nanoscience and Nanotechnology including graduate student Yonatan Ossia with seven other members and led by Prof. Uri Banin, have now come up with an innovative solution to this problem. By developing a system of an “artificial molecule” made of two coupled semiconductor nanocrystals that emit light in two different colors, fast and instantaneous color switching was achieved. 

Banin said that “our research is a big leap forward in nanomaterials for optoelectronics. This is an important step in our exposition of the idea of “nanocrystal chemistry” launched just a few years ago in our research group in which nanocrystals are building blocks of artificial molecules with exciting new functionalities.

Being able to switch colors so quickly and efficiently on the nanoscale as we have achieved has enormous possibilities. It could revolutionize advanced displays and create color-switchable single photon sources.” 

When taking color-emitting semiconductors to the nanoscale (a nano is one-billionth of a meter, 100,000 times smaller than a human hair), an effect called quantum confinement comes into play. Changing the size of the nanocrystal modifies the color of the emitted light, so bright light sources can be obtained covering the entire visible spectrum.

Because of the unique color tunability of such nanocrystals and their easy fabrication and manipulation using wet chemistry, they are already widely used in high-quality commercial displays, giving them excellent color quality along with significant energy-saving characteristics.

But until now, achieving different colors such as needed for the different RGB pixels (composed of red, green and blue subpixels that light up at different intensities to create different colors and use in electronic displays like TVs, computer monitors, lighting, and digital cameras) required the use of different nanocrystals for each specific color. However, dynamic switching between the different colors was not possible.

Although color tuning of single colloidal nanocrystals which behave as “artificial atoms” has been studied and implemented in prototype optoelectronic devices, changing colors actively has been challenging because of the diminished brightness inherently accompanying the effect that produced only a slight shift of the color. 

The research team overcame this limitation, by creating a novel molecule with two emission centers in which an electric field can tune the relative emission from each center, changing the color, yet, without losing brightness.

The artificial molecule can be made such that one of its constituent nanocrystals is tuned to emit “green” light, while the other “red” light. The emission of this new dual color emitting artificial molecule is sensitive to external voltage inducing an electric field – one polarity of the field induces emission of light from the “red” center, and switching the field to the other polarity, the color emission is switched instantaneously to “green”, and vice versa.

This color-switching phenomenon is reversible and immediate, as it does not include any structural motion of the molecule. 

Link to the publication: www.jpost.com

Pulmonary embolism (PE) is currently the third leading cause of death from heart disease after myocardial infarction (heart attacks) and stroke. Early diagnosis is essential as a staggering one in three deaths occur within the first few hours compared with only 7% of deaths in properly diagnosed and treated cases.

Catheter-directed thrombolysis (CDT) is a procedure that involves delivering low doses of medication directly into the pulmonary arteries using a catheter. However, due to the lack of comprehensive research on its safety and efficacy, treatment guidelines for CDT vary because of this uncertainty.

In a comparative analysis of different treatments for pulmonary embolisms, Israeli researchers have made a significant breakthrough. The study found that CDT was associated with a 55% decreased risk of death as well as lower risks of major bleeding and brain bleeds among 65%, when compared to other treatment options.

Dr. Bruria Hirsh Raccah, Clinical pharmacist in the cardiology department at the Hadassah Medical Center and researcher at the Hebrew University of Jerusalem and a co-author of the study, cautions that "further research is necessary before drawing definitive conclusions. However, the findings indicate that CDT should be considered the preferred treatment among eligible patients, given its safety and effectiveness, especially when compared to the higher toxicity of systemic thrombolysis.”

“Although this study should be interpreted as hypothesis generating, our findings suggest that, among patients eligible for CDT and where facilities exist, CDT should be the preferred treatment, given its safety and effectiveness, and given the higher toxicity of systemic thrombolysis” writes Dr. Bruria Hirsh Raccah, a researcher at the Hebrew University of Jerusalem, Jerusalem, Israel, with coauthors.

The study was part of Stav Yanko’s dissertation at the Hebrew University of Jerusalem.

The study was co-authored by Bruria Hirsch Raccah, Stav Yanko and other researchers from Hadassah Medical Center.

“Mortality and safety assessment of catheter-directed thrombolysis compared with systemic thrombolysis and anticoagulation in patients with intermediate or high-risk pulmonary embolism: systematic review and network meta-analysis” was published June 19, 2023. https://www.medscape.com/viewarticle/993506?src=

Researchers from the Hebrew University of Jerusalem and the University of California, Berkeley, have made progress in understanding the puzzling affliction known as unilateral neglect, where stroke victims lose conscious awareness of half of what their eyes perceive. The scientists have identified a region in the brain where sustained visual images are retained for a few seconds. By recording brain activity from electrodes placed on patients' brains, they discovered that visual areas of the brain retain information about a perceived object at a low level of activity for an extended period, suggesting a neural basis for stable perception. The prefrontal and parietal cortexes become active when something new is perceived, while the occipitotemporal area of the visual cortex maintains a sustained but low level of activity. These findings provide insights into the difference between perceiving something and being consciously aware of perceiving it, which could have implications for coma patients and the development of treatments for consciousness disorders.

More than a quarter of all stroke victims develop a bizarre disorder — they lose conscious awareness of half of all that their eyes perceive.

After a stroke in the brain's right half, for example, a person might eat only what's on the right side of the plate because they're unaware of the other half. The person may see only the right half of a photo and ignore a person on their left side.

Surprisingly, though, such stroke victims can emotionally react to the entire photo or scene. Their brains seem to be taking it all in, but these people are consciously aware of only half the world.

This puzzling affliction, called unilateral neglect, highlights a longstanding question in brain science: What's the difference between perceiving something and being aware or conscious of perceiving it? You may not consciously note that you passed a shoe store while scrolling through your Instagram feed, yet you started searching online for shoe sales. Your brain records things that you don't consciously take note of.

Neuroscientists from the Hebrew University of Jerusalem and the University of California, Berkeley, now report that they may have found the region of the brain where these sustained visual images are retained during the few seconds we perceive them. They published their findings last week in the journal Cell Reports.

"Consciousness, and in particular, visual experience, is the most fundamental thing that everyone feels from the moment they open their eyes when they wake up in the morning to the moment they go to sleep," said Hebrew University graduate student Gal Vishne, lead author of the paper. "Our study is about your everyday experience."

While the findings do not yet explain how we can be unaware of what we perceive, studies like these could have practical applications in the future, perhaps allowing doctors to tell from a coma patient's brain activity whether the person is still aware of the outside world and potentially able to improve. Understanding consciousness may also help doctors develop treatments for disorders of consciousness.

"The inspiration for my whole scientific career comes from patients with stroke who suffer from unilateral neglect, where they just ignore half of the world," said senior author Leon Deouell, a Hebrew University professor of psychology and member of the Edmond and Lily Safra Center for brain research. "That actually triggered my whole interest in the question of conscious awareness. How is it that you can have the information, but still not acknowledge it as something that you're subjectively experiencing, not act upon it, not move your eyes to it, not grab it? What is required for something not only to be sensed by the brain, but for you to have a subjective experience? Understanding that would eventually help us understand what is missing in the cognitive system and in the brains of patients who have this kind of a syndrome."

"We are adding a piece to the puzzle of consciousness — how things remain in your mind's eye for you to act on," added Robert Knight, also a senior author and a UC Berkeley professor of psychology and member of the Helen Wills Neuroscience Institute.

The brain has a transient and a sustained response

Deouell noted that for some six decades, electrical studies of the human brain have almost solely concentrated on the initial surge of activity after something is perceived. But this spike dies out after about 300 or 400 milliseconds, while we often look at and are consciously aware of things for seconds or longer.

"That leaves a whole lot of time which is not explained in neural terms," he said.

In search of longer-lasting activity, the neuroscientists obtained consent to run tests on 10 people whose skulls were being opened so that electrodes could be placed on the brain surface to track neural activity associated with epileptic seizures. The researchers recorded brain activity from the electrodes as they showed different images to the patients on a computer screen for different lengths of time, up to 1.5 seconds. The patients were asked to press a button when they saw an occasional item of clothing to ensure that they truly were paying attention.

Most methods used to record neural activity in humans, such as functional MRI (fMRI) or electroencephalography (EEG), only allow researchers to make detailed inferences about where brain activity is happening or when, but not both. By employing electrodes implanted inside the skull, the Hebrew University/UC Berkeley researchers were able to bridge this gap.

After analyzing the data using machine learning, the team found that, contrary to earlier studies that saw only a brief burst of activity in the brain when something new was perceived, the visual areas of the brain actually retained information about the percept at a low level of activity for much longer. The sustained pattern of neural activity was similar to the pattern of the initial activity and changed when a person viewed a different image.

"This stable representation suggests a neural basis for stable perception over time, despite the changing level of activity," Deouell said.

Unlike some earlier studies, they found that the prefrontal and parietal cortexes in the front of the brain become active only when something new is perceived, with information disappearing entirely within half a second (500 milliseconds), even for a much longer stimulus.

The occipitotemporal area of the visual cortex in the back of the brain also becomes very active briefly — for about 300 milliseconds — and then drops to a sustained but low level, about 10% to 20% of the initial spike. But the pattern of activity does not go away; it actually lasts unaltered about as long as a person views an image.

"The frontal cortex is involved in the detection of something new," Deouell explained. "But you also see an ongoing representation in the higher-level sensory regions."

The sequence of events in the brain could be interpreted in various ways. Knight and Vishne lean toward the idea that conscious awareness comes when the prefrontal cortex accesses the sustained activity in the visual cortex. Deouell suspects that consciousness arises from connections among many areas of the brain, the prefrontal cortex being just one of them.

The team's findings have been confirmed by a group that calls itself the Cogitate Consortium. Though the consortium's results are still awaiting peer review, they were described in a June event in New York City that was billed as a face-off between two "leading" theories of consciousness. Both the Cell Reports results and the unpublished results could fit either theory of consciousness.

"That adversarial collaboration involves two theories out of something like 22 current theories of consciousness," Deouell cautioned. "Many theories usually means that we don't understand."

Nevertheless, the two studies and other ongoing studies that are part of the adversarial collaboration initiated by the Templeton Foundation could lead to a true, testable theory of consciousness.

"Regarding the predictions of the two theories which we were able to test, both are correct. But looking at the broader picture, none of the theories in their current form work, even though we find each to have some grain of truth, at the moment," Vishne said. "With so much still unknown about the neural basis of consciousness, we believe that more data should be collected before a new phoenix can rise out of the ashes of the previous theories. "

Future studies planned by Deouell and Knight will explore the electrical activity associated with consciousness in other regions of the brain, such as the areas that deal with memory and emotions.

Edden Gerber is also a co-author of the paper. The study was supported by the U.S.-Israel Binational Science Foundation (2013070) and the National Institute of Neurological Disorders and Stroke of the National Institutes of Health (R01 NS021135).

In the pursuit of justice, law enforcement agencies heavily rely on forensic evidence, with DNA testing constituting the cornerstone of modern investigations. While the scientific and technological advancements in DNA testing have been extensively studied, there is scant evidence regarding how the availability of DNA evidence influences prosecutors’ decisions to move cases forward.

To address this knowledge gap, the research team created a unique database by combining data from the Forensics Division of the Israel Police, which documented the presence or absence of DNA profiles in criminal cases (n = 9862), with data on each case’s subsequent indictment decision from 2008 to 2019.

This extensive dataset’s analysis yielded significant insights into the impact of DNA evidence on criminal prosecutions. The researchers discovered that roughly 15% of all criminal cases presented to the prosecutor’s office were ultimately prosecuted. In stark contrast, the criminal justice system advanced approximately 55% of cases with DNA profiles. This effect demonstrates the significant influence DNA evidence has on the decisions of prosecutors.

The findings highlight the significance of using a scientific approach to prosecute offenders, recognising the value DNA evidence brings to the criminal justice system. However, the researchers caution against the indiscriminate use of DNA evidence and emphasise the necessity of prudence. DNA evidence is a potent tool, but it is not infallible; therefore, its use in the legal system must be carefully considered. The study encourages a balanced approach that harnesses the benefits of DNA evidence while acknowledging its limitations.

This research contributes to the ongoing dialogue surrounding the role of forensic evidence in criminal investigations, specifically highlighting the impact of DNA profiles on prosecution decisions in Israel. The findings have implications for law enforcement agencies, legal professionals, and policymakers involved in the pursuit of justice.

The study, titled “ The role of DNA in criminal indictments in Israel" was published in the Journal of Forensic Sciences - https://onlinelibrary.wiley.com/doi/pdf/10.1111/1556-4029.15327

The research team consisted of Esther Buchnik, Institute of Criminology, The Hebrew University of Jerusalem, Prof. Barak Ariel Institute of Criminology, University of Cambridge, Prof. Avi Domb Faculty of Medicine and the Institute of Criminology, The Hebrew University of Jerusalem, Nir Treves Faculty of Medicine, The Hebrew University of Jerusalem, Dr. Ron Gafny, Division of Identification and Forensic Science, Israel Police.

Methodology: The records examined were from 2008-2019. Over the study period, the average rate of indictment in all cases was approximately 15.1%, with a relatively stable variance [standard deviation (SD) of 0.8%]. However, 45.9% of criminal cases with DNA were subsequently indicted, with a steady yet clear increase over time (from 26.3% to 53.6% in 2019; SD = 11.8%).

The Hebrew University of Jerusalem is Israel’s premier academic and research institution. With over 23,000 students from 80 countries, it is a hub for advancing scientific knowledge and holds a significant role in Israel’s civilian scientific research output, accounting for nearly 40% of it and has received over 11,000 patents. The university’s faculty and alumni have earned eight Nobel Prizes and a Fields Medal, underscoring their contributions to ground-breaking discoveries. In the global arena, the Hebrew University ranks 77th according to the Shanghai Ranking, making it the top-ranked Israeli institution. To learn more about the university’s academic programs, research initiatives, and achievements, visit the official website at http://new.huji.ac.il/en