The next concept—scale, proportion, and quantity—concerns the sizes of things and the mathematical relationships among disparate elements. The next four concepts—systems and system models, energy and matter flows, structure and function, and stability and change—are interrelated in that the first is illuminated by the other three. Each concept also stands alone as one that occurs in virtually all areas of science and is an important consideration for engineered systems as well. Regardless of the labels or organizational schemes used in these documents, all of them stress that it is important for students to come to recognize the concepts common to so many areas of science and engineering.
For a shorter, less technical discussion, see Chapter 2. Site selection and management Advection frosts are associated with wind and little vertical stratification of temperature. During advection frosts, the lowest temperatures are usually observed on the middle and higher portions of hillsides that are open and exposed to the wind.
Higher night-time temperatures are observed on the down-wind sides of hills and in low spots that are sheltered from the wind. Radiation frosts are associated with calm conditions or light wind and katabatic i.
Cold air accumulates in depressions, where the air becomes vertically stratified with temperature increasing with height.
In radiation frosts, higher night-time temperatures are observed on hilltops and on upper middle sections of hillsides that are free from obstacles to block cold air drainage.
However, in some locations, they can block cold air drainage and favour stratification and cold air ponding. Every location is unique and the advantages and disadvantages of proximity to rocky masses and canopy covers must be considered separately at each location.
Site selection is the single most important method of frost protection. Factors to consider are cold air drainage, slope and aspect, and soil type. Most growers are aware of some spots that are more prone to damage than others.
Typically, low spots in the local topography have colder temperatures and hence more damage. However, damage can sometimes occur in one section of a cropped area and not in another without apparent topographical differences.
In some cases, this might be due to differences in soil type, which can affect the conduction and storage of heat in the soil. Of course, management of the soil and cover crops can also affect heat storage and damage.
Although not commonly cited as a site selection factor, proximity to grasses and other plants with high concentrations of ice-nucleating bacteria can also be a factor affecting frost damage.
However, the advantages from orienting crop rows to enhance cold air drainage must be evaluated against the disadvantages due to more erosion and other inconveniences.
For example, grass and plant stubble in areas upslope from a crop. One universal characteristic of productive growers is that they are all aware of the potential for frost damage and they thoroughly investigate a site before planting a crop that might be damaged by subzero temperatures.
For some crops, it is desirable to have cold temperatures e. The trick is to find locations that have a good microclimate for high-quality production without losing yield to damaging temperatures. If subzero temperatures are intermittent and infrequent, then using an active protection method to avoid damage during frost events while enjoying the beneficial effects of cold temperatures is a good economic strategy.
However, to determine cost-effectiveness, the cost of protection and potential losses must be balanced against enhanced revenues from a high quality product. In general, crops are grown where the weather conditions are favourable, and potential frost damage is often the limiting factor.
For example, citrus is grown on the east side of the San Joaquin Valley in California USA to a large extent because extensive frost damage is infrequent. The San Joaquin Valley has a gentle slope downwards about km from the east edge to the centre of the valley with the citrus growing area located in the eastern-most 30 km.
December through February is the main rainy season for this region, so the sky is often cloudy. However, even during non-cloudy periods, the San Joaquin Valley is prone to fog formation.
Both cloud cover and fog increase downward long-wave radiation and lessen net radiation losses. The occurrence of a radiation frost is rare during cloudy or foggy conditions because the net radiation losses are reduced. On rare occasions, subzero temperatures occur during cloudy conditions associated with an advection frost.
However, radiation frosts are considerably more common than advection frosts in the area. In addition to clouds and fog reducing the frequency of subzero temperatures, cold air also drains westward away from the citrus area.
The elevation is higher in the east i. On a regional scale, the cold air drains slowly to the west. Consequently, no experienced grower would attempt to grow citrus further to the west where potential frost damage is considerably higher due to regional scale cold air drainage.
A third reason for growing citrus in this area is that the fog often clears in the afternoon, so sunlight can strike the soil and plants to store some heat during the day. This would not be the case on the west side of the valley because a mountain range to the west blocks radiation during the late afternoon and evening.
On the east side of the valley, the slope of the land is generally facing to the west, so the receipt of energy per unit area from the sun is better on the east than the west side of the valley in the afternoon.
The first step in selecting a site for a new planting is to talk to local people about what crops and varieties are appropriate for the area.
Local growers and extension advisors often have a good feeling for which locations might be problematic. One should avoid planting in areas where low, ground fogs form first. Low ground fogs are radiation fogs, and, like radiation frosts, they tend to form in the coldest spots.science investigates cause-and-effect relationships by seeking the mechanisms that underlie them.
The next concept—scale, proportion, and quantity—concerns the sizes of things and the mathematical relationships among disparate elements. Someone is changing the past for financial gain/ or altering the past and causing rifts in other areas by happenstance. I sent you one story about an arcade game here is one that hit me hard and close to home a couple of years ago.
Investigate the effect of different temperatures on the activity of pepsin (enzyme) with HCL and egg white? Today I've been tracking down the origin of the term "Greenhouse Effect".
The term itself is problematic, because it only works as a weak metaphor: both the atmosphere and a greenhouse let the sun's rays through, and then trap some of the resulting heat.
But the mechanisms are different. A . LabBench Activity Enzyme Catalysis. by Theresa Knapp Holtzclaw. Introduction. Enzymes catalyze reactions by lowering the activation energy necessary for a reaction to occur. Employers don't have to provide air conditioning, but sensible ones should recognise the effect of heat on productivity.
Photograph: Sipa Press/Rex Features.