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The fast progression of the now 175 kilometre long crack has had glaciologists around the world wondering when and how the ice will break away from the front of the ice shelf. It has just 20 kilometres left to go.
The crack has been advancing rapidly since 2014 but suddenly picked up speed last year. At its fastest it advanced 18 kilometres in just two weeks in December 2016, and grew another ten kilometres in January this year.
The worst case scenario is that the crack reaches a point known as the Bawden Ice Rise, a pinning point at the northern part of the ice shelf. In this scenario the remaining ice shelf flows faster towards the sea, exerting even more force on the existing cracks in Larsen C.
Borstad is planning a field trip to the ice shelf this year to further investigate how these suture zones halt ice cracks in their tracks. But this trip may be brought forward if the iceberg suddenly breaks away.
Visual examination of the HES concrete patches was conducted each year between 1994 and 1998, usually between the months of August and November. The survey teams consisted of experienced personnel, and care was taken to maintain uniformity in the data collection, as much as possible, over the entire performance monitoring period. The main data items of interest during the visual examination process included recording the progression of pavement distress within each patch, with special focus on materials-related distresses. The distresses were recorded through a variety of means, including mapping distresses, recording any changes in condition, and taking pHotos and videos of the section. In addition to monitoring the condition of concrete, for the North Carolina section it was also meaningful to collect and analyze pavement performance data such as faulting, transverse cracking, and joint spalling. At each site, the respective State DOT provided necessary traffic control to perform the distress surveys.
The Illinois sections exhibit some map cracking. The level of cracking did not change substantially over the monitoring period, altHough some progression of map cracking was noted over the years. One plausible cause for this distress is the potential use of deicing salts on these patches. Subjectively, at least, the sections generally seemed more deteriorated in 1998 than in 1994 (perhaps the impression is due to more scaling). However, as noted earlier, these changes were difficult to quantify. Figures 35 through 39 in appendix A sHow that both Illinois sections had some transverse cracking. The structural crack in the IL-2 section existed since 1994, and no significant changes in progression or deterioration of the crack occurred over the monitoring period. Other cracks are a result of the interconnecting of map cracks. A minor progression of these cracks occurred over the monitoring period, but none appeared to have progressed to a working, structural crack.
The Nebraska sections have a few transverse cracks, which have existed since 1994 (see figures 40 through 44 in appendix A). A modest increase in map cracking was noticed in 1998. The map cracking occurred mostly along the joints and cracks and around the cores. The pattern cracking appeared characteristic of ASR, which is known to occur in the area. It is interesting to note, However, that map cracking appeared to be a problem only on the repair slabs (not just the SHRP repairs, but also other repairs in the area). The original concrete, placed in 1957, did not exhibit any signs of map cracking.
The one experimental patch in New York remained in excellent condition with no signs of map cracking or scaling over the entire monitoring period. The scaling and map cracking prevalent in patches located at other sites did not affect this patch. It was reported in the original SHRP study that deicing salts were not used on this section between 1991 and 1993. (1)
The North Carolina section is in excellent condition with no signs of map cracking or scaling. The concrete condition did not change over the monitoring period. The North Carolina patch is relatively long compared to the other patches, so monitoring the pavement performance is more meaningful. The pavement performance data from the North Carolina section are summarized in table 6. The transverse cracks present at the time of construction (due to delay in sawing joints) progressed over time from low to high severity in some locations. The section also exhibits some joint spalling and faulting. However, the levels of these distresses remained relatively low and their condition remained virtually unchanged over the entire performance monitoring period.
crack that is not the result of external forces and has no effect on structural resistance or integrity; usually the result of shrinkage (plastic, settlement and drying), thermal changes, or internal chemical reaction.
1) intersecting cracks that extend below the surface of hardened concrete; caused by shrinkage of the drying surface concrete that is restrained by concrete at greater depths where either little or no shrinkage occurs; vary in width from fine and barely visible to open and well-defined; or 2) the chief symptom of chemical reaction between alkalies in cement and mineral constituents in aggregate within hardened concrete; due to differential rate of volume change in different portions of the concrete; cracking is usually random and on a fairly large scale, and in severe instances the cracks may reach a width of 0.50 in. (12.7 mm); also known as pattern cracking. (See also cracks, checking; and crazing.)
According to the United Kingdom-based Project MIDAS, which has spent years surveying the ice shelf, a 2,000-square-mile chunk of ice is hanging on by just a thread. If the crack continues to grow at its current rate, the ice shelf could collapse in just a matter of months, forming one of the largest icebergs ever recorded, George Dvorsky reports for Gizmodo.
Though the Cracks (or Crack) of Doom was literally a crevice within Mount Doom, there's a secondary level to the name. As Tolkien points out in his notes for translators, the phrase comes from Shakespeare, specifically from Macbeth Act 4, scene 1: 'What, will the line stretch out to the crack of doom?'. In that context, the 'crack' is a loud sound (either a thunderclap or the sound of a trumpet) announcing the arrival of judgement day (or 'doomsday'). So, Tolkien's choice of this name for the fiery fissure of Orodruin is rather more portentous than its simple literal meaning might suggest.
Go beyond the iconic crack to learn how this State House bell was transformed into an extraordinary symbol. Abolitionists, women's suffrage advocates and Civil Rights leaders took inspiration from the inscription on this bell. Plan your visit to the Liberty Bell Center to allow time to view the exhibits, see the film, and gaze upon the famous cracked bell. No tickets are required and hours vary seasonally.
From Signal to Symbol The State House bell, now known as the Liberty Bell, rang in the tower of the Pennsylvania State House. Today, we call that building Independence Hall. Speaker of the Pennsylvania Assembly Isaac Norris first ordered a bell for the bell tower in 1751 from the Whitechapel Foundry in London. That bell cracked on the first test ring. Local metalworkers John Pass and John Stow melted down that bell and cast a new one right here in Philadelphia. It's this bell that would ring to call lawmakers to their meetings and the townspeople together to hear the reading of the news. Benjamin Franklin wrote to Catherine Ray in 1755, "Adieu, the Bell rings, and I must go among the Grave ones and talk Politicks." It's not until the 1830s that the old State House bell would begin to take on significance as a symbol of liberty.
The Crack No one recorded when or why the Liberty Bell first cracked, but the most likely explanation is that a narrow split developed in the early 1840s after nearly 90 years of hard use. In 1846, when the city decided to repair the bell prior to George Washington's birthday holiday (February 23), metal workers widened the thin crack to prevent its farther spread and restore the tone of the bell using a technique called "stop drilling". The wide "crack" in the Liberty Bell is actually the repair job! Look carefully and you'll see over 40 drill bit marks in that wide "crack". But, the repair was not successful. The Public Ledger newspaper reported that the repair failed when another fissure developed. This second crack, running from the abbreviation for "Philadelphia" up through the word "Liberty", silenced the bell forever. No one living today has heard the bell ring freely with its clapper, but computer modeling provides some clues into the sound of the Liberty Bell.
In this study, we experimentally demonstrate fabrication of ultra-smooth and crystalline barium titanate (BTO) films on magnesium oxide (MgO) substrates by engineering lattice strain and crystal structure via thermal treatment. We observe that oxygen-depleted deposition allows growth of highly strained BTO films on MgO substrates with crack-free surface. In addition, post-thermal treatment relaxes strain, resulting in an enhancement of ferroelectricity. Surface roughening of the BTO films caused by recrystallization during post-thermal treatment is controlled by chemical-mechanical polishing (CMP) to retain their initial ultra-smooth surfaces. From Raman spectroscopy, reciprocal space map (RSM), and capacitance-voltage (C-V) curve measurements, we confirm that the ferroelectricity of BTO films strongly depend on the relaxation of lattice strain and the phase transition from a-axis to c-axis oriented crystal structure.
Schoettle, C. (2013) Sustained macroscopic deflected cracking in Nickel based superalloys : mechanism and design criteria. University of Southampton, Faculty of Engineering and the Environment, Doctoral Thesis, 307pp. 2b1af7f3a8