TSC Ratings provides exclusive stock, ETF and mutual fund ratings and commentary based on award-winning, proprietary tools. Its "safety first" approach to investing aims to reduce risk while seeking solid outperformance on a total return basis.

The following ratings changes were generated on Tuesday, April 28.

We've upgraded

Albemarle

(ALB) - Get Report

from hold to buy, driven by its solid financial position based on a variety of debt and liquidity measures that we have evaluated. We feel these strengths outweigh the fact that the company has had lackluster performance in the stock itself.

Revenue fell 27.2% since the same quarter a year ago, and EPS are also down. Albemarle's debt-to-equity ratio of 0.9 is somewhat low overall but high compared with the industry average. Net income decreased 59.9% compared with the year-ago quarter, from $63.3 million to $25.4 million. Return on equity also decreased, implying a minor weakness in the organization. Albemarle's gross profit margin of 23.9% has decreased from the year-ago quarter, and the 5.2% net profit margin trails the industry average.

We've downgraded

China Unicom

(CHU) - Get Report

from hold to sell, driven by its feeble growth in its earnings per share, disappointing return on equity and generally disappointing historical performance in the stock itself.

EPS declined 75% in the most recent quarter compared with the year-ago quarter, and we anticipate that the company's declining EPS should continue in the coming year. ROE also decreased compared with the year-ago quarter. China Unicom's debt-to-equity ratio of 0.2 is below the industry average. The 0.2 quick ratio is weak and implies a lack of ability to pay short-term obligations. The 46.5% gross profit margin is strong, though it has decreased from the year-ago quarter. The net profit margin of 28% outperformed the industry average.

Shares have tumbled 49.7% over the past year, underperforming the

S&P 500

. Naturally, the overall market trend is bound to be a significant factor, and in one sense, the stock's sharp decline last year is a positive for future investors, making it cheaper (in proportion to its earnings over the past year) than most other stocks in its industry. But due to other concerns, we feel the stock is still not a good buy right now.

We've downgraded

DryShips

(DRYS) - Get Report

from hold to sell, driven by its deteriorating net income, generally weak debt management, disappointing return on equity, weak operating cash flow and generally disappointing historical performance in the stock itself.

Net income fell from $194.4 million in the year-ago quarter to -$1 billion in the most recent quarter. The 2.5 debt-to-equity ratio is above the industry average. The 0.3 quick ratio implies an inability to cover short-term cash needs. ROE decreased compared with the year-ago quarter, and net operating cash flow fell 122.4% to -$42.2 million.

Shares have tumbled 92.4% over the past year, underperforming the S&P 500.Naturally, the overall market trend is bound to be a significant factor. However, in one sense, the stock's sharp decline last year is a positive for future investors, making it cheaper (in proportion to its earnings over the past year) than most other stocks in its industry. But due to other concerns, we feel the stock is still not a good buy right now.

We've upgraded

Plum Creek Timber

(PCL)

from hold to buy, driven by itsrevenue growth, notable return on equity, expanding profit margins, good cash flow from operations and compelling growth in net income. Although the company may harbor some minor weaknesses, we feel they are unlikely to have a significant impact on results.

Revenue rose by 29.5% since the year-ago quarter, and EPS are up. ROE also rose, a sign of strength within the company. The 36.4% gross profit margin has increased since the same period last year, and the 33.4% net profit margin outperformed the industry average. Net operating cash flow increased to $284 million compared with the year-ago quarter, and net income increased 313% to $157 million.

We've downgraded

Southwestern Energy

(SWN) - Get Report

from buy to hold. Strengths include the company's revenue growth, good cash flow from operations and largely solid financial position with reasonable debt levels by most measures. However, we also find weaknesses including a decline in the stock price during the past year, deteriorating net income and disappointing return on equity.

Revenue increased by 3.2% since the same quarter last year, though EPS declined. Net operating cash flow increased 37.1% to $407.3 million. The 0.3 debt-to-equity ratio is low but is higher than the industry average. ROE decreased compared with the year-ago quarter.

Other ratings changes include

Qualcomm

(QCOM) - Get Report

, downgraded from buy to hold, and

Archer Daniels Midland

(ADM) - Get Report

, downgraded from buy to hold.

All ratings changes from April 28 are listed below.

Note: Our quantitative model makes stock recommendations based on GAAP figures that may differ materially from data as reported by the companies themselves. As a result, rating changes are occasionally driven by so-called nonrecurring items. As always, we urge readers to use TSC Ratings' reports in conjunction with additional information to construct their opinions on the value that should be placed on any given stock.

TheStreet.com Ratings, recently cited for Best Stock Selection from October 2007 through February 2009 , is an independent research provider that combines fundamental and technical analysis to offer investors tremendous value in volatile times. To see how your portfolio can use this research,

click here now!