Image source: Mark Adriane/Unsplash
- Mobile devices used both indoors and out may benefit from a new energy collection system that thrives on mixed and changing lighting conditions.
- Inexpensive new collection cells are said to be twice as efficient as commercial solar cells.
- The system's "shadow effect" would also maker it useful as a sensor for tracking traffic.
For all of its promise, solar energy depends on the capture of light, and the more the better. For residents of sunny climes, that's great, with rooftop collection panels, and solar farms built by utilities in wide open, sunny spaces that can provide power to the rest of us. Now, though, a team of scientists at the National University of Singapore (NUS) has announced success at deriving energy from…shadows.
We've got plenty of them everywhere. "Shadows are omnipresent, and we often take them for granted," says research team leader Tan Swee Ching, who notes how shadows are usually anathema for energy collection. "In conventional photovoltaic or optoelectronic applications where a steady source of light is used to power devices, the presence of shadows is undesirable, since it degrades the performance of devices." His team has come up with something quite different, and Tan claims of their shadow-effect energy generator (SEG) that, "This novel concept of harvesting energy in the presence of shadows is unprecedented."
The research is published in the journal Energy & Environmental Science.
How it works
Image source: Royal Society of Chemistry/NUS
The energy produced by the SEG is generated from the differential between shadowed and lit areas. "In this work," says Tan. "We capitalized on the illumination contrast caused by shadows as an indirect source of power. The contrast in illumination induces a voltage difference between the shadow and illuminated sections, resulting in an electric current."
SEG cells are less expensive to produce than solar cells. Each SEG cell is a thin film of gold on a silicon wafer, and an entire system is a set of four of these cells arrayed on a flexible, transparent plastic film. Experiments suggest the system, in use, is twice as efficient as commercial solar cells.
An SEG cell's shadow effect works best when it is half in light and half in shadow, "as this gives enough area for charge generation and collection respectively," says co-team leader Andrew Wee. When the SEG is entirely in shadow or in light, it doesn't produce a charge.
Gold in them that shadows
Image source: stockfour/Dayna More/Dmitry Naumov/Shutterstock/Big Think
To be sure, the amount of energy that NUS researchers have thus far extracted is small, but it's enough to power a digital watch. The researchers envision the SEG system harvesting ambient light to power smart phones and AR glasses that are used both outdoors and indoors. While such devices can run on solar batteries, solar is only replenished outdoors, and the SEG could "scavenge energy from both illumination and shadows associated with low light intensities to maximize the efficiency of energy harvesting," says Tan. It seems clear that we're on the cusp of the era of wearables — AR visionwear, smart fabrics, smart watches, and so on — and so Tan considers the arrival of the SEG "exciting and timely."
The researchers also note an additional application for which the SEG seems a natural: It can function as a self-powered sensor for monitoring moving objects. The shadow caused by a passing object would trigger the SEG sensor, which can then record the event.
Next up for the team is investigating constructing cells using other, less costly materials than gold to make them even less expensive to produce.
Image source: Vaccaro et al, 2020/Harvard Medical School
- A study provides further confirmation that a prolonged lack of sleep can result in early mortality.
- Surprisingly, the direct cause seems to be a buildup of Reactive Oxygen Species in the gut produced by sleeplessness.
- When the buildup is neutralized, a normal lifespan is restored.
We don't have to tell you what it feels like when you don't get enough sleep. A night or two of that can be miserable; long-term sleeplessness is out-and-out debilitating. Though we know from personal experience that we need sleep — our cognitive, metabolic, cardiovascular, and immune functioning depend on it — a lack of it does more than just make you feel like you want to die. It can actually kill you, according to study of rats published in 1989. But why?
A new study answers that question, and in an unexpected way. It appears that the sleeplessness/death connection has nothing to do with the brain or nervous system as many have assumed — it happens in your gut. Equally amazing, the study's authors were able to reverse the ill effects with antioxidants.
The study, from researchers at Harvard Medical School (HMS), is published in the journal Cell.
An unexpected culprit
The new research examines the mechanisms at play in sleep-deprived fruit flies and in mice — long-term sleep-deprivation experiments with humans are considered ethically iffy.
What the scientists found is that death from sleep deprivation is always preceded by a buildup of Reactive Oxygen Species (ROS) in the gut. These are not, as their name implies, living organisms. ROS are reactive molecules that are part of the immune system's response to invading microbes, and recent research suggests they're paradoxically key players in normal cell signal transduction and cell cycling as well. However, having an excess of ROS leads to oxidative stress, which is linked to "macromolecular damage and is implicated in various disease states such as atherosclerosis, diabetes, cancer, neurodegeneration, and aging." To prevent this, cellular defenses typically maintain a balance between ROS production and removal.
"We took an unbiased approach and searched throughout the body for indicators of damage from sleep deprivation," says senior study author Dragana Rogulja, admitting, "We were surprised to find it was the gut that plays a key role in causing death." The accumulation occurred in both sleep-deprived fruit flies and mice.
"Even more surprising," Rogulja recalls, "we found that premature death could be prevented. Each morning, we would all gather around to look at the flies, with disbelief to be honest. What we saw is that every time we could neutralize ROS in the gut, we could rescue the flies." Fruit flies given any of 11 antioxidant compounds — including melatonin, lipoic acid and NAD — that neutralize ROS buildups remained active and lived a normal length of time in spite of sleep deprivation. (The researchers note that these antioxidants did not extend the lifespans of non-sleep deprived control subjects.)
Image source: Tomasz Klejdysz/Shutterstock/Big Think
The experiments
The study's tests were managed by co-first authors Alexandra Vaccaro and Yosef Kaplan Dor, both research fellows at HMS.
You may wonder how you compel a fruit fly to sleep, or for that matter, how you keep one awake. The researchers ascertained that fruit flies doze off in response to being shaken, and thus were the control subjects induced to snooze in their individual, warmed tubes. Each subject occupied its own 29 °C (84F) tube.
For their sleepless cohort, fruit flies were genetically manipulated to express a heat-sensitive protein in specific neurons. These neurons are known to suppress sleep, and did so — the fruit flies' activity levels, or lack thereof, were tracked using infrared beams.
Starting at Day 10 of sleep deprivation, fruit flies began dying, with all of them dead by Day 20. Control flies lived up to 40 days.
The scientists sought out markers that would indicate cell damage in their sleepless subjects. They saw no difference in brain tissue and elsewhere between the well-rested and sleep-deprived fruit flies, with the exception of one fruit fly.
However, in the guts of sleep-deprived fruit flies was a massive accumulation of ROS, which peaked around Day 10. Says Vaccaro, "We found that sleep-deprived flies were dying at the same pace, every time, and when we looked at markers of cell damage and death, the one tissue that really stood out was the gut." She adds, "I remember when we did the first experiment, you could immediately tell under the microscope that there was a striking difference. That almost never happens in lab research."
The experiments were repeated with mice who were gently kept awake for five days. Again, ROS built up over time in their small and large intestines but nowhere else.
As noted above, the administering of antioxidants alleviated the effect of the ROS buildup. In addition, flies that were modified to overproduce gut antioxidant enzymes were found to be immune to the damaging effects of sleep deprivation.
The research leaves some important questions unanswered. Says Kaplan Dor, "We still don't know why sleep loss causes ROS accumulation in the gut, and why this is lethal." He hypothesizes, "Sleep deprivation could directly affect the gut, but the trigger may also originate in the brain. Similarly, death could be due to damage in the gut or because high levels of ROS have systemic effects, or some combination of these."
The HMS researchers are now investigating the chemical pathways by which sleep-deprivation triggers the ROS buildup, and the means by which the ROS wreak cell havoc.
"We need to understand the biology of how sleep deprivation damages the body so that we can find ways to prevent this harm," says Rogulja.
Referring to the value of this study to humans, she notes,"So many of us are chronically sleep deprived. Even if we know staying up late every night is bad, we still do it. We believe we've identified a central issue that, when eliminated, allows for survival without sleep, at least in fruit flies."
