epidemic

The Black Death, a bacterial epidemic that wiped out more than 1 in 3 Europeans from 1347 to 1351, was not an equal-opportunity destroyer। http://louis4j4sheehan4esquire.blogspot.comA new report finds that the disease disproportionately took the lives of physically frail people, rather than indiscriminately killing off individuals regardless of their health। http://louis4j4sheehan4esquire.blogspot.com

Sharon DeWitte of the University at Albany, N।Y., and James W. Wood of Pennsylvania State University in University Park examined 490 skeletons from London's East Smithfield cemetery, established in 1348 or 1349 solely to bury Black Death victims. The researchers looked for any of four types of bone damage or deformation that have been linked to infections or poor nutrition early in life. http://louis4j4sheehan4esquire.blogspot.com

For comparison, DeWitte and Wood also studied 291 pre-Black Death skeletons from cemeteries of two medieval Danish towns.

The scientists estimated each individual's age at death and used a computer model to calculate the extent to which frailty contributed to death in the two populations.

Physical infirmities greatly raised the risk of dying for Danes unexposed to the Black Death, the scientists report in the Feb. 5 Proceedings of the National Academy of Sciences. For instance, Danes with certain lower-leg lesions exhibited more than five times the risk of dying as their peers without such damage did.

Frailty also showed a strong, but less pronounced, link to death among Britons exposed to the epidemic. Individuals who incurred lower-leg damage before exposure to the Black Death were 50 percent more likely to die during the epidemic than were their non-damaged peers.

The new findings challenge assumptions that Black Death cemeteries contain a representative cross-section of the population from that time.

Forecasting a snow avalanche takes more than measuring the angle of a mountain slope, researchers report in the July 11 Science। Whether an avalanche happens might also depend on how the snow cracks and collapses, the study suggests। http://louis-j-sheehan.com

“The new theory could be a breakthrough in understanding what is going on at the very moment when an avalanche begins,” says University of Edinburgh physicist Joachim Heierli, lead author of the study. It “gives hints on what snow properties to look for to anticipate the risk of triggering a slab avalanche.”

Slab avalanches are the most common and most dangerous because a slab of snow breaks loose and cascades to the slope’s bottom. By modeling this avalanche type the team found that snow fractures much more easily than previously thought. Also, friction between snow layers may be more important in avalanche dynamics than once thought.

“Friction may not stop the fracture from spreading but may stop the avalanche,” Heierli says.

Also, gravity pulling down along the slope is less important than the compression of the snow, the team reports.

All cracked upScientists capture a sudden cracking of the snowpack, which is a clear sign of stress and instability. The way the snow fractures can portend whether the snow layers will collapse in on themselves or slide as a slab down the slope below as an avalanche.A. Duclos, www.data-avalanche.org

In a snow pile, a brittle, collapsible layer sits between a solid, dense snow slab on top and a rigid snow base below। The way the brittle, middle snow layer fractures when it’s disturbed controls whether a snow pile will shear off leading to a violent slab avalanche or will collapse under its own weight। http://louis-j-sheehan.com

Scientists had previously thought that slab avalanches start when shear cracks along the brittle, middle layer of a snowpack spread and that the angle of the slope, and therefore the gravity tugging on the slope, would drive the avalanche.

According to this argument, says Heierli, the critical crack size to start an avalanche should increase as the slope angle decreases. But recent field experiments done by other researchers on snowpacks in Canada showed instead that, in general, the size of the crack in the brittle, middle layer required to start an avalanche increased or remained constant as slope angles increased.

Heierli’s team tried to address this discrepancy between the experiments and the theory of slab avalanche triggers by modeling both the gravitational tug on the snow along the slope angle and the downward pull of gravity perpendicular to the slope, finding the perpendicular pull was more important.

“Some layers inside the snow are a very frail network of ice grains with lots of space in between,” Heierli says. “Some arrangements may crumble like a house of cards because some grains or fragments fall into the space between other ice grains. Then a cavity forms between the two layers.”

Modeling the development of these cavities, or “anticracks,” led the team to conclude that fractures caused by snow crumbling can spread over large areas and create an avalanche similar to what was seen in the most recent field experiments, the study reports.

“This research is really an entirely new paradigm for how the fractures that result in snow avalanches work,” says Karl Birkeland, a scientist with the U.S. Forest Service’s National Avalanche Center. “And, these findings better fit with what we observe about avalanches in the field.”

The new findings also suggest that horizontal snow layers can fracture more easily than once thought and that there is no measured, minimum slope angle to start a snow slide.

“If moving over a flat snow cover, you may trigger a remote avalanche on the hill above you making it come down on you or others,” Heierli says. “Experienced backcountry skiers know this already, but now they may better understand how it can happen.”

Birkeland notes that the new model offers a new way to think about how avalanches are triggered and might lead to better tests for predicting snow slides in the field.

dispatch

MAY 28TH.—Showers and sunshine.

Grant has crossed the Pamunky, and Lee is at the Yellow Tavern—not more than six miles from the city. http://louis1j1sheehan1esquire.blogspot.comThe hostile armies are only a few miles apart, and the GREAT BATTLE may occur at any time, at any hour; and we shall hear both the artillery and musketry from my dwelling.

All is quiet on the south side of the river. Nothing from Georgia, except a short address from Gen. Johnston to the army, stating that, having the enemy now where he wants him, he will lead the soldiers to battle.

War and famine develop some of the worst instincts of our nature. For five days the government has been selling meal, by the peck, for $12: and yet those who have been purchasing have endeavored to keep it a secret! And the government turns extortioner, making $45 profit per bushel out of the necessities of the people!

I saw a dispatch, to-day, from Gen. Johnston to his Chief Commissary, at Atlanta, ordering him, after reserving ten days’ rations, to send the rest of the stores to Augusta!

It is said Mr. Memminger and certain members of Congress have in readiness the means of sudden flight, in the event of Grant’s forcing his way into the city.http://louis1j1sheehan1esquire.blogspot.com

It is thought, to-day, that Bragg will resign. If he does, then the President will be humiliated; for the attacks on Bragg are meant principally for Mr. Davis. But I doubt the story; I don’t think the President will permit Bragg to retire before his enemies, unless affairs become desperate by the defeat of our army in this vicinity.